Systems and methods for communication of channel state information

ABSTRACT

Aspects of the present disclosure relate to techniques for communicating Channel State Information (CSI) feedback. According to certain aspects, a method for wireless communications is provided. The method may include determining a modulation coding scheme (MCS) or a rate for receiving channel state information. The method may further include transmitting a frame comprising a control field indicating the determined MCS or the determined rate and at least one field indicating that at least a portion of channel state information is requested.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.61/387,542, filed Sep. 29, 2010; U.S. Provisional Application No.61/389,495, filed Oct. 4, 2010; U.S. Provisional Application No.61/405,283, filed Oct. 21, 2010; U.S. Provisional Application No.61/422,098, filed Dec. 10, 2010; U.S. Provisional Application No.61/432,115, filed Jan. 12, 2011; U.S. Provisional Application No.61/405,194, filed Oct. 20, 2010; and U.S. Provisional Application No.61/409,645, filed Nov. 3, 2010; the entire content of each of which isincorporated herein by reference. This application further claims thebenefit of U.S. Provisional Application No. 61/414,651, filed Nov. 17,2010. This application is related to U.S. application Ser. No.13/247,023, titled “SYSTEMS AND METHODS FOR COMMUNICATION OF CHANNELSTATE INFORMATION,” filed on even date herewith, U.S. application Ser.No. 13/247,047, titled “SYSTEMS AND METHODS FOR COMMUNICATION OF CHANNELSTATE INFORMATION,” filed on even date herewith, U.S. application Ser.No. 13/247,062, titled “SYSTEMS AND METHODS FOR COMMUNICATION OF CHANNELSTATE INFORMATION,” filed on even date herewith, U.S. application Ser.No. 13/247,100, titled “SYSTEMS, METHODS AND APPARATUS FOR DETERMININGCONTROL FIELD AND MODULATION CODING SCHEME INFORMATION,” filed on evendate herewith, U.S. application Ser. No. 13/247,124, titled “SYSTEMS,METHODS AND APPARATUS FOR DETERMINING CONTROL FIELD AND MODULATIONCODING SCHEME INFORMATION,” filed on even date herewith, U.S.application Ser. No. 13/247,144, titled “SYSTEMS, METHODS AND APPARATUSFOR DETERMINING CONTROL FIELD AND MODULATION CODING SCHEME INFORMATION,”filed on even date herewith, each of which are incorporated herein byreference, in their entirety.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to methods of communicatingChannel State Information (CSI).

2. Background

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. Multiple Input Multiple Output (MIMO) technologyrepresents one such approach that has recently emerged as a populartechnique for next generation communication systems. MIMO technology hasbeen adopted in several emerging wireless communications standards suchas the Institute of Electrical and Electronics Engineers (IEEE) 802.11standard. The IEEE 802.11 denotes a set of Wireless Local Area Network(WLAN) air interface standards developed by the IEEE 802.11 committeefor short-range communications (e.g., tens of meters to a few hundredmeters).

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system can provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

In wireless networks with a single Access Point (AP) and multiple userstations (STAs), concurrent transmissions may occur on multiple channelstoward different stations, both in the uplink and downlink direction.Many challenges are present in such systems.

SUMMARY

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus comprises a processing systemconfigured to determine a modulation coding scheme (MCS) or a rate forreceiving channel state information. The apparatus comprises atransmitter configured to transmit a frame comprising a control fieldindicating the determined MCS or the determined rate and at least onefield indicating that at least a portion of channel state information isrequested.

Certain aspects of the present disclosure provide a method for wirelesscommunication. The method comprises determining a modulation codingscheme (MCS) or a rate for receiving channel state information. Themethod comprises transmitting a frame comprising a control fieldindicating the determined MCS or the determined rate and at least onefield indicating that at least a portion of channel state information isrequested.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus comprises means for determining amodulation coding scheme (MCS) or a rate for receiving channel stateinformation. The apparatus comprises means for transmitting a framecomprising a control field indicating the determined MCS or thedetermined rate and at least one field indicating that at least aportion of channel state information is requested.

Certain aspects of the present disclosure provide a computer programproduct for wirelessly communicating comprising a computer readablemedium comprising instructions. The instructions when executed cause anapparatus to determine a modulation coding scheme (MCS) or a rate forreceiving channel state information. The instructions when executedcause an apparatus to transmit a frame comprising a control fieldindicating the determined MCS or the determined rate and at least onefield indicating that at least a portion of channel state information isrequested.

Certain aspects of the present disclosure provide an access point forwireless communications. The apparatus comprises an antenna. The accesspoint comprises a processing system configured to determine a modulationcoding scheme (MCS) or a rate for receiving channel state information.The access point comprises a transmitter configured to transmit, via theantenna, a frame comprising a control field indicating the determinedMCS or the determined rate and at least one field indicating that atleast a portion of channel state information is requested.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a diagram of a wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates an aspect of a Channel State Information (CSI)feedback protocol.

FIG. 5 illustrates an aspect of an NDPA frame.

FIGS. 6A-6C illustrate aspects of an STA information field.

FIGS. 7A-7C illustrate aspects of STA information included in the STAinformation field illustrated in FIGS. 6A-6C.

FIG. 8 illustrates an aspect of an NDPA frame.

FIGS. 9A and 9B illustrate aspects of a control wrapper.

FIG. 10 illustrates an aspect of a control wrapper.

FIG. 11 illustrates an aspect of a CSI report message for communicatingCSI feedback.

FIGS. 12A-12E illustrate aspects of a control field for soundingfeedback.

FIG. 13 illustrates an aspect of an access point.

FIG. 14 illustrates an aspect of a method of communication.

FIG. 15 illustrates an aspect of a method of communication.

FIG. 16 illustrates an aspect of a method of communication.

FIG. 17 illustrates an aspect of an access terminal.

FIG. 18 illustrates an aspect of a method of communication.

FIG. 19 illustrates an aspect of a method of communication.

FIG. 20 illustrates an aspect of a method of communication.

FIG. 21 illustrates an aspect of a method of communication.

FIG. 22 illustrates an aspect of a method of communication.

FIG. 23 illustrates an aspect of a method of communication.

FIG. 24 illustrates an aspect of a method of communication.

FIG. 25 illustrates a block diagram of an example user terminal inaccordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosureherein, whether implemented independently of or combined with any otheraspect of the disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the disclosure is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the disclosure set forth herein. It shouldbe understood that any aspect of the disclosure disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the described aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of aspects. The detaileddescription and drawings are merely illustrative of the disclosurerather than limiting.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal. A TDMA system may implement GSM orsome other standards known in the art. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An OFDM system may implement IEEE 802.11 or some otherstandards known in the art. An SC-FDMA system may utilize interleavedFDMA (IFDMA) to transmit on sub-carriers that are distributed across thesystem bandwidth, localized FDMA (LFDMA) to transmit on a block ofadjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multipleblocks of adjacent sub-carriers. In general, modulation symbols are sentin the frequency domain with OFDM and in the time domain with SC-FDMA. ASC-FDMA system may implement 3GPP-LTE (3^(rd) Generation PartnershipProject Long Term Evolution) or other standards.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, a user station, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a Session Initiation Protocol(“SIP”) phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, aportable computing device (e.g., a personal data assistant), anentertainment device (e.g., a music or video device, or a satelliteradio), a global positioning system device, or any other suitable devicethat is configured to communicate via a wireless or wired medium. Insome aspects the node is a wireless node. Such wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as the Internet or a cellular network) via a wired orwireless communication link.

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system 100 with access points and user terminals. For simplicity,only one access point 110 is shown in FIG. 1. An access point isgenerally a fixed station that communicates with the user terminals andmay also be referred to as a base station or using some otherterminology. A user terminal may be fixed or mobile and may also bereferred to as a mobile station or a wireless device, or using someother terminology. The access point 110 may communicate with one or moreuser terminals 120 at any given moment on the downlink and uplink. Thedownlink (i.e., forward link) is the communication link from the accesspoint to the user terminals, and the uplink (i.e., reverse link) is thecommunication link from the user terminals to the access point. A userterminal may also communicate peer-to-peer with another user terminal. Asystem controller 130 couples to and provides coordination and controlfor the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects,the AP 110 may be configured to communicate with both SDMA and non-SDMAuser terminals. This approach may conveniently allow older versions ofuser terminals (“legacy” stations) that do not support SDMA to remaindeployed in an enterprise, extending their useful lifetime, whileallowing newer SDMA user terminals to be introduced as deemedappropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsub-bands with OFDM, and so on. Each selected user terminal may transmituser-specific data to and/or receive user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same number of antennas, or one or more user terminals may havea different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. The MIMO system 100may also utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, where each time slotmay be assigned to a different user terminal 120.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 ap. The user terminal 120m is equipped with N_(ut,m) antennas 252 ma through 252 mu, and the userterminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu.The access point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. The user terminal 120 is a transmittingentity for the uplink and a receiving entity for the downlink. As usedherein, a “transmitting entity” is an independently operated apparatusor device capable of transmitting data via a wireless channel, and a“receiving entity” is an independently operated apparatus or devicecapable of receiving data via a wireless channel. In the followingdescription, the subscript “dn” denotes the downlink, the subscript “up”denotes the uplink, N_(up) user terminals are selected for simultaneoustransmission on the uplink, and N_(dn) user terminals are selected forsimultaneous transmission on the downlink. N_(up) may or may not beequal to N_(dn), and N_(up) and N_(dn) may be static values or maychange for each scheduling interval. Beam-steering or some other spatialprocessing technique may be used at the access point 110 and/or the userterminal 120.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. The TX data processor288 processes (e.g., encodes, interleaves, and modulates) the trafficdata for the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252, forexample to transmit to the access point 110.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals may perform spatial processingon its respective data symbol stream and transmit its respective set oftransmit symbol streams on the uplink to the access point 110.

At the access point 110, N_(ap) antennas 224 a through 224 ap receivethe uplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing may be performed in accordancewith the channel correlation matrix inversion (CCMI), minimum meansquare error (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at the access point 110, a TX data processor 210receives traffic data from a data source 208 for N_(dn) user terminalsscheduled for downlink transmission, control data from a controller 230,and possibly other data from a scheduler 234. The various types of datamay be sent on different transport channels. TX data processor 210processes (e.g., encodes, interleaves, and modulates) the traffic datafor each user terminal based on the rate selected for that userterminal. The TX data processor 210 provides N_(dn) downlink data symbolstreams for the N_(dn) user terminals. A TX spatial processor 220performs spatial processing (such as a precoding or beamforming) on theN_(dn) downlink data symbol streams, and provides N_(ap) transmit symbolstreams for the N_(ap) antennas. Each transmitter unit 222 receives andprocesses a respective transmit symbol stream to generate a downlinksignal. N_(ap) transmitter units 222 may provide N_(ap) downlink signalsfor transmission from N_(ap) antennas 224, for example to transmit tothe user terminals 120.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from the access point 110. Each receiver unit 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol streamfor the user terminal 120. The receiver spatial processing may beperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). The controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point 110. The controllers 230and 280 may also control the operation of various processing units atthe access point 110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may implement an access point 110 or a user terminal120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 may perform logical and arithmetic operations based onprogram instructions stored within the memory 306. The instructions inthe memory 306 may be executable to implement the methods describedherein.

The processor 304 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

In some aspects, the wireless system 100 illustrated in FIG. 1 operatesin accordance with IEEE 802.11ac wireless communications standard. TheIEEE 802.11ac represents a IEEE 802.11 amendment that allows for higherthroughput in IEEE 802.11 wireless networks. The higher throughput maybe realized through several measures, for example parallel transmissionsto multiple stations (STAs) at once. In some aspects, a wider channelbandwidth (e.g., 80 MHz or 160 MHz) is used. The IEEE 802.11ac standardmay also sometimes be referred to as Very High Throughput (VHT) wirelesscommunications standard.

Certain aspects of the present disclosure support a low-overhead methodfor communicating Channel State Information (CSI) or feedback therefore.For example, such information may be communicated between the userterminals 120 and the access point 110 in the wireless system 100.Certain aspects of the present disclosure further support packet formatsfor a Null Data Packet Announcement (NDPA), CSI poll, and CSI feedback.Some aspects support a communication indicating whether CSI has bereceived and/or stored, for example by or at an AP. This information maybe used by an STA, for example, to determine whether to send further CSIand/or whether to adjust parameters for transmitting the CSI. Someaspects support a communication indicating whether CSI is beingtransmitted, for example by an STA. This information may be used by anAP, for example, to determine how to transmit requests for requests forthe CSI and/or whether to adjust parameters for transmitting the CSIrequests. In some cases, the CSI feedback may be too large to be carriedin a single Media Access Control (MAC) protocol data unit (MPDU) or aPhysical Layer (PHY) protocol data unit (PPDU). Certain aspects of thepresent disclosure further support a protocol for CSI feedbacksegmentation. In the following description, reference is made to a userstation (STA). As described above, a STA may comprise a user terminal,for example the user terminal 120 or the wireless device 302.

Channel State Information

FIG. 4 illustrates an aspect of a Channel State Information (CSI)feedback protocol 400. An access point (AP) may transmit to one or moreuser stations (STAs) a Null Data Packet Announcement (NDPA) frame 402followed by a Null Data Packet (NDP) frame 404 after a Short Inter-FrameSymbol (SIFS) period 406. The NDPA frame 402 may comprise AssociationIdentifiers (AIDs) of the STAs that should transmit computed CSIfeedback messages to the AP, as will be described in additional detailbelow.

Those STAs that are not identified in the NDPA may ignore the followingNDP frame 404. The NDP frame 404 may comprise a sounding frame utilizedby each of the STAs to compute corresponding CSI feedback. A firstlisted STA within the NDPA frame 402 may transmit CSI Feedback 408subsequent to a SIFS period after the transmission of the NDP frame 404,as illustrated in FIG. 4. In some aspects, the CSI Feedback 408comprises only a portion of the complete CSI feedback for the firstlisted STA. For example, when the complete CSI feedback is too large tobe transmitted in a data unit such as an MPDU or a PPDU, the portionincluded in the CSI Feedback 408 may be small enough for transmission inthe data unit. In these aspects, the AP may transmit a CSI Poll 412 torequest an additional portion of the complete CSI feedback from thefirst listed STA. The first listed STA may then transmit another portionsuch as CSI Feedback 414 in response to the CSI Poll 412. This processof polling an STA may continue until all portions of the complete CSIfeedback have been received.

In some aspects, a CSI Poll may be sent by the AP to another STA listedin the NDPA frame to request the other STA to send CSI feedback. Forexample, if the first listed STA in the NDPA frame 402 divides itscomplete CSI feedback into the two portions of CSI Feedback 408, 414,then the AP may request another STA listed in the NDPA frame 402 tobegin transmission of CSI feedback with CSI Poll 416. In response, theother STA may transmit CSI Feedback 418, which may be complete CSIfeedback or a portion of the complete CSI feedback for the other STA.Any number of STAs may be identified in the NDPA frame 402, as will bediscussed in additional detail below, and the AP may transmit any numberof CSI polls and/or receive any number of CSI feedbacks or portionsthereof.

After the NDPA frame 402 is transmitted, the AP may transmit a secondNDPA frame 422 to again request CSI feedback. The STAs from which CSIfeedback is requested by the NDPA frame 422 may be different or the sameas the STAs from which CSI feedback is requested by the NDPA frame 402.The number of STAs from which CSI feedback is requested in the NDPAframes 402, 422 may be the same or may vary.

In some aspects, the NDPA frame 422 is transmitted after CSI feedbackhas been received from all of the STAs identified in the NDPA frame 402.In some aspects, the NDPA frame 422 is transmitted a certain time periodafter the NDPA frame 402, regardless of whether CSI feedback has beenreceived from all of the STAs identified in the NDPA frame 402. In someaspects, the NDPA frame 422 is transmitted after a polling message suchas a CSI poll has been sent to all of the STAs identified in the NDPAframe 402. In some aspects, the NDPA frame 422 may identify one or moreSTAs that are not identified in the NDPA frame 402, or may identify asubset of the STAs that are identified in the NDPA frame 402. Thus, theAP may request CSI feedback from an STA with the NDPA frame 422 whilestill receiving CSI feedback from one or more STAs identified in theNDPA frame 402. In some aspects, the NDPA frame 422 may transmitted bythe AP in response to a certain event, or the transmission of the NDPAframe 422 may be triggered by an action of the AP or another device.

FIG. 5 illustrates an aspect of an NDPA frame, for example the NDPAframe 422. In some aspects, the NDPA frame 422 may be referred to as aCSI request message, which may be of type control frame. The NDPA frame422 may comprise one or more of a frame control field 502, a durationfield 504, an RA broadcast field 506, a TA field 508, a CSI sequencefield 512, an STA information field 514, and a CRC field 516. The NDPAframe 422 may be transmitted or broadcast by the AP, as described above.The NDPA frame 402 may be formatted or configured similar to the NDPAframe 422.

In the illustrated aspect, the frame control field 502 comprises 16bits. Also in the illustrated aspect, the duration field 504 comprises16 bits and may include a length of the NDPA frame 422. The CRC field516 in the illustrated aspect comprises 32 bits and may comprise datafor determining a Cyclic Redundancy Check (CRC).

In the illustrated aspect, the RA broadcast field 506 comprises 48 bits.The RA broadcast field 506 may comprise a broadcast/multicast addressfor multiple STAs. For example, the RA broadcast field 506 may include agroup address, where a plurality of STAs belong to the group. In suchaspect, each STA may identify if it is being addressed based on thegroup address. In other aspects, the RA broadcast field 506 may insteadidentify a single STA, for example by indicating a MAC address of anintended STA. In some aspects, the RA broadcast field 506 may insteadcomprise or be referred to as a DA (destination address) field.

In the illustrated aspect, the TA field 508 comprises 48 bits. The TAfield 508 may comprise an address or identifier of a device transmittingthe NDPA frame 422, for example an address of the transmitting AP. Insome aspects, the TA field 508 may instead comprise or be referred to asan SA (source address) field.

In the illustrated aspect, the CSI sequence field 512 comprises 8 bits.The CSI sequence field 512 may comprise a sequence number for the NDPAframe 422 or another descriptor uniquely identifying the NDPA frame 422.

In the illustrated aspect, the length of the STA information field 514may vary. The STA information field 514 may include information for eachSTA from which CSI or other such feedback information is requested.

FIGS. 6A-6C illustrate aspects of an STA information field, for examplethe STA information field 514. In the aspect illustrated in FIG. 6A,when the RA broadcast field 506 of the NDPA frame 422 identifies asingle STA, the STA information field 514 a will include information 602for only that identified STA. In another aspect illustrated in FIGS. 6Band 6C, where the RA broadcast field 506 of the NDPA frame 422 comprisesa broadcast/multicast address for multiple STAs, for example,information for each STA from which the AP is requesting feedback willbe included in the STA information field 514. In FIG. 6B, the AP isrequesting CSI from STAs 1-4, and information 612-618 for each STA isincluded in the STA information field 514 b. In FIG. 6C, in contrast,the AP is requesting CSI only from STAs 5 and 6, and information 622 and624 is included in the STA information field 514 c. In some aspects, abroadcast/multicast or group address may be included in the RA broadcastfield 506, but information for only a single STA included in the STAinformation field 514. In this way, a broadcast/multicast address may beincluded in the NDPA frame 422 for ease of processing and/or uniformity,but a single STA addressed.

FIGS. 7A-7C illustrate aspects of STA information included in the STAinformation field 514. Any one of the STA information 602-624illustrated in FIGS. 6A-6C may be formatted as illustrated in any ofFIGS. 7A-7C. As an example, STA information 612 is illustrated in FIG.7.

The STA information 612 may communicate to an STA parameters that theSTA may use to report CSI. In some aspects, the CSI returned by the STAis referred to as sounding feedback (SF). In these aspects, the STAinformation 612 may include information or data for the STA to determineand/or calculate SF based on a sounding frame included in the NDP frame404 illustrated in FIG. 4, for example. In some aspects, the STAinformation 612 may be used to determine no to send SF, or to send aform of SF that requires less data.

In the aspect illustrated in FIG. 7A, STA information 612 a may compriseone or more of an AID field 702, an Nss field 704, an Ng field 706, acoefficient field 712, and a codebook field 714, a last SF receivedfield 722, and a last SF stored field 724. In some aspects, the STAinformation 612 a further comprises a reserved field 732 that includesbits in addition to those assigned to the fields 702-724 that may beused for any of a variety of purposes. In some aspects, the fields702-732 are arranged in an order that differs from the order illustratedin FIG. 7A.

In the illustrated aspect, the AID field 702 comprises 11 bits and mayinclude an AID. As described above, an AID may comprise an AssociationIdentifier of an STA. The AID may comprise any data or descriptor thatuniquely identifies the STA. For example, a physical address such as aMAC address may be included in the AID. In some aspects, each of thefields 704-724 may include information or data indicating parameters forthe STA identified by the AID field 702 to use in calculating,determining, or generating CSI or SF.

In the illustrated aspect, the Nss field 704 comprises at least 3 bits.The Nss field 704 may indicate a number of spatial channels or streams(e.g., Eigen modes) of CSI feedback to be computed at the STA identifiedby the AID field 702.

In the illustrated aspect, the Ng field 706 comprises at least 3 bits.In some aspect, the Ng field 706 comprises at least 2 bits. The Ng field706 may indicate a grouping of tones on which the STA identified by theAID field 702 is to generate CSI feedback. For example, the tones maycorrespond to sub-carriers in an OFDM system.

In the illustrated aspect, the coefficient field 712 comprises at least3 bits. In some aspects, the coefficient field 712 comprises one or morebits. The coefficient field 712 may indicate a coefficient size, whichmay correspond to a quantization used by the STA identified by the AIDfield 702 for matrix entries of the CSI, as will be described inadditional detail below. In some aspects, the coefficient field 712 isomitted. For example, the NDPA 402 may indicate that the CSI isformatted as a form of compressed feedback, in which case a coefficientsize may not be included.

In the illustrated aspect, the codebook field 714 comprises at least 3bits. In some aspects, the codebook field 714 comprises one or morebits. The codebook field 714 may indicate a quantization for angles thatthe STA identified by the AID field 702 should use for SF.

In the illustrated aspect, the last SF received field 722 comprises atleast 1 bit. The last SF received field may indicate whether the AP hasreceived SF from the STA identified by the AID field 702 subsequent tosending a previous NDPA frame. For example, in the aspect discussed withrespect to FIG. 4, the NDPA frame 402 was transmitted to several STAs torequest channel state information. A second STA identified in the NDPAframe 422 transmitted the CSI feedback 418. In the NDPA frame 422, ifthe AID field 702 in the STA information 612 a identifies the secondSTA, then last SF received field 722 may indicate whether the APreceived the CSI feedback 418. For example, the last SF received fieldmay be set to a value of 0 if the CSI feedback 418 was not received, andmay be set to a value of 1 if the CSI feedback 418 was received. Inother aspects, these values may be reversed. In some aspects, the lastSF received field 722 is used as an acknowledgement of receipt of thelast sounding feedback that the AP polled for.

In some aspects, the last SF received field comprises at least 8 bitsand may include a sequence number. In this aspect, the last SF receivedfield indicates the sequence number corresponding to the last CSIfeedback transmitted. For example, the NDPA frame 422 illustrated inFIG. 5 includes a sequence number for the NDPA frame 422 or anotherdescriptor uniquely identifying the NDPA frame 422 in the CSI sequencefield 512. If SF is received in response to the NDPA frame 422 from anSTA—in some aspects, the SF includes the sequence number or otheridentifier—a following NDPA frame may include the sequence number orother identifier in a last SF received filed of an STA informationidentifying the STA from which the SF was received.

Channel state information transmitted by an STA may not have beenreceived by an AP for any of a variety of reasons. For example, dataconflicts, channel interference, or physical obstacles may all prevent acommunication such as CSI feedback from being received, or reduce thelikelihood that the CSI feedback is accurately received. In someaspects, even in situations where the AP receives CSI from an STA, thelast SF field will be set to indicate that the CSI feedback was notreceived if the CSI feedback cannot be accurately decoded or processed.

The last SF received field 722 may be used by the STA identified by theAID field 702 for any number of purposes. For example, if the STAtransmitted SF in response to the NDPA frame 402, but the last SFreceived field 722 indicates that the SF was not received by the AP, theSTA may determine that there was an error in the transmission. Inresponse, the STA may retransmit the previous SF. As another example, ifthe STA did not transmit SF in response to the NDPA frame 402, but thelast SF received field 722 indicates that SF was received, the STA maydetermine that the received SF is erroneous and may send a communicationto the AP instructing the AP to discard the received SF.

In some aspects, the last SF received field 722 may be used to adjust arate used to send SF. For example, when the last SF received field 722indicates that SF was not received even though the STA transmitted theSF, the STA may reduce a PHY rate for sending a subsequent SF.Similarly, when the last SF received field 722 indicates that apreviously transmitted SF was successfully received, the STA mayincrease a PHY rate for sending a subsequent SF. In this way, a rateused to send the SF may be continually adjusted or tuned for increasedperformance. In some aspects, another parameter or characteristicbesides the rate may be adjusted based on whether a previous SF wasproperly received. For example, a modulation used for sending the SF maybe changed if the previous SF was not properly received.

In some aspects, the STA adjusts a rate only after a series of SFs wasproperly received, or after the series of SFs was improperly received.For example, the STA may increase a rate after receiving a certainnumber of NDPA frames having a last SF received field that indicatesthat SF was properly received. In some aspects, if a series of SFs wasnot properly received, for example as indicated by CSI last receivedfields in a series of NDPA frames, the STA may transmit a communicationto the AP to indicate that the AP should refrain from sending anyadditional requests for CSI. In this way, network resources consumed bytransmitting the NDPA to the STA may be conserved when the AP does notappear to be properly receiving any CSI from the STA.

In some aspects, the rate used by the STA to send the sounding feedbackis determined from a rate of a polling message. For example, the rateused to send the CSI poll 416 in the aspect illustrated in FIG. 4 may beused to send the CSI feedback 418. As another example, the rate used tothe send the CSI poll 416 may be adjusted up or down based on whether aprevious SF was received, as indicated by the last SF received field,for example.

Returning to the description of the STA information 612 a illustrated inFIG. 7A, the last SF stored field 724 comprises at least 1 bit. The lastSF stored field 724 may indicate whether the AP has stored the last SFreceived from the STA identified by the AID field 702. Thus, in someaspects, the last SF stored field 724 may indicate whether the AP hasstored SF received from the STA subsequent to sending a previous NDPAframe. For example, in the aspect discussed with respect to FIG. 4, theNDPA frame 402 was transmitted to several STAs to request channel stateinformation. A second STA identified in the NDPA frame 422 transmittedthe CSI feedback 418. In the NDPA frame 422, if the AID field 702 in theSTA information 612 a identifies the second STA, then last SF storedfield 724 may indicate whether the AP stored the CSI feedback 418. Forexample, the last SF stored field may be set to a value of 0 if the CSIfeedback 418 was not stored, and may be set to a value of 1 if the CSIfeedback 418 was stored. In other aspects, these values may be reversed.

In some aspects, the last SF stored field comprises at least 8 bits andmay include a sequence number. In this aspect, the last SF stored fieldindicates the sequence number corresponding to the last CSI feedbacktransmitted. For example, the NDPA frame 422 illustrated in FIG. 5includes a sequence number for the NDPA frame 422 or another descriptoruniquely identifying the NDPA frame 422 in the CSI sequence field 512.If SF received from an STA has been stored subsequent to the NDPA frame422—in some aspects, the SF includes the sequence number or otheridentifier—a following NDPA frame may include the sequence number orother identifier in a last SF stored filed of an STA informationidentifying the STA from which the SF was received.

Channel state information transmitted by an STA may not have been storedby an AP for any of a variety of reasons. For example, when the CSIhasn't been received or is received improperly, the CSI can't be storedby the AP. In some aspects, however, even properly received CSI may notbe stored. For example, an AP may not have enough memory to store theCSI. As another example, the AP may determine not to store the CSI whena specific time period has elapsed since requesting the CSI, or when agiven time period has elapsed since the CSI was determined by the STA.In this way, the CSI may have “timed out” and may not be stored. In someaspects, the AP may delete stored CSI that has “timed out.” Whentransmitting the next NDPA, the AP may indicate in the last SF storedfield for the STA that transmitted the deleted CSI that the CSI has notbeen stored.

The last SF stored field 724 may be used by the STA identified by theAID field 702 for any number of purposes. For example, if the STAtransmitted SF in response to the NDPA frame 402, but the last SF storedfield 724 indicates that the SF was not stored by the AP, the STA mayretransmit the previous SF.

As another example, if the last SF stored field 724 indicates that theprevious SF was stored and the STA determines that the channel for whichCSI is requested has changed less than a threshold amount, or determinesthat the CSI has changed less than a threshold amount, the STA maydetermine that the stored CSI and a current CSI are substantially thesame and may not to send any CSI in response to the NDPA frame 422. Inthis circumstance, the STA may instead send a communication to the APindicating that no CSI will be transmitted, for example as describedbelow. Omitting the CSI may conserve network resources and increase thespeed and/or reliability of communications within the network.

In some aspects where the last SF stored field 724 indicates that theprevious SF was stored, the STA may transmit information representing adifference between the stored SF and current SF. In some aspects,complete CSI feedback may comprise a matrix or data indicative thereof.In some aspects, the matrix comprises a plurality of Eigen modes,singular vectors, or singular values. As described above, the STA maydetermine a spatial filter matrix based on a downlink channel responsematrix H_(dn,m) for that STA. Feedback information (e.g., the downlinkeigenvectors, eigenvalues, SNR estimates, and so on) may be thereby betransmitted, for example to the AP. Thus, channel state informationand/or SF may be represented as a matrix. In some aspects, a differencebetween a previous SF and a current SF may also be represented by amatrix. The difference matrix, however, may require fewer bytes torepresent. Thus, sending a difference CSI instead of a complete CSI mayalso conserve network resources.

In some aspects, when the last SF received field 722 indicates that thelast SF that the AP polled has not been received, the last SF storedfield 724 will always indicate that the AP has not stored the last SFpolled for. For example, when the last SF received field 722 and thelast SF stored field 724 are implemented as bits as described above, thelast SF stored field 724 will always have a value of 0 when the last SFreceived field 722 has a value of 0. In other aspects, when the SFreceived field 722 indicates that the last SF that the AP polled has notbeen received, the last SF stored field 724 may be used to indicate thata previously stored SF is still being stored by the AP. For example,when the last SF received field 722 and the last SF stored field 724 areimplemented as bits as described above and the last SF received field722 has a value of 0, the last SF stored field 724 may be set to 1 toindicate that a previously stored SF is still being stored and may beswitched to 0 to indicate that a previously stored SF has been deletedor that a new complete SF is requested.

Some aspects use indicators other than the fields 704-724 to indicateparameters to an STA that the STA may use to report CSI. In one aspect,a bit or series of bits in the STA information 612 a may be used by theSTA to lookup the relevant parameters. The STA may have parametersstored or may retrieve parameters corresponding to one or more of theNss field 704, Ng field 706, coefficient field 712, and codebook field714 based on such bits in the STA information 612 a.

FIG. 7B illustrates another aspect 612 b of the STA information 612. TheSTA information 612 b is illustrated as including the fields 702-724 and732 included in the STA information 612 a, as well as an MU/SU field726. In the illustrated aspect, the MU/SU field 726 comprises at least 1bit. This field may indicates whether the STA identified by the AIDfield 702 is requested to provide single user (SU) or multi-user (MU)feedback. In this way, the AP may separately notify each STA identifiedin the NDPA frame 422 whether SU or MU feedback is requested from thatrespective STA.

In some aspects, one or more of the fields 702-732 are omitted from theSTA information 612. Further, additional fields may be included in theSTA information 612. In some aspects, some of the bits in the STAinformation 612 are reserved for other or future uses. For example, STAinformation 612 c illustrated in FIG. 7C shows an aspect including theAID field 702, a field 752 having one or more bits that have beenreserved for future use, and a previous SF stored field 754. Theprevious SF stored field may indicate when the AP has stored the last SFit had polled from the STA identified in the AID field 702. In someaspects, the previous SF stored field 754 may be configured similar toand/or used similar to the last SF stored field 724.

In comparison to the aspect illustrated in FIG. 7B, another aspect fornotifying STAs whether MU or SU feedback is requested is illustrated inFIG. 8. In the aspect illustrated in FIG. 8, an MU/SU field 522 isincluded in an NDPA frame 422 a. The NDPA frame 422 a may be formattedor configured similar to the NDPA frame 422, with the exception that theMU/SU field 522 is added to the NDPA frame 422 a such that the MU/SUfield 522 is separate from the STA information field 514. The MU/SUfield 522 may be used as a “global” indicator to signify whether SU orMU feedback is requested from all of the STAs identified in the STAinformation field 514.

In some aspects, the AP may require or request that the CSI betransmitted using a particular modulation coding scheme (MCS). FIGS. 9Aand 9B illustrate aspects of a frame including information fordetermining the MCS. In the aspect illustrated in FIG. 9A, frame 900 acomprises an NDPA frame that has been “wrapped” in a control wrapper.Thus, the frame 900 a may be used to request CSI from an STA, forexample in addition to or in place of the NDPA frame 422.

In the illustrated aspect, the frame 900 a includes the frame controlfield 502, duration field 504, RA broadcast field 506, SA field 508, CSIsequence field 512, STA information field 514, and CRC field 516 thatare included in the NDPA 422. In addition, the frame 900 a includes acarried frame control field 902 and an HT-control field 904. In theillustrated aspect, the carried frame control field 902 comprises atleast 2 bits, and the HT-control field 904 comprises at least 4 bits.

The HT-control field 904 may comprise information indicating an MCS forthe STAs identified in the STA information field 514 to use whentransmitting SF. In some aspects, the HT-control field 604 comprises alink adaption control field including information which the STAs may useto determine the MCS. In some aspects, the link adaption control fieldincludes a TRQ (Training Request) field, an MAI (MCS Request or AntennaSelection Indication) field, an MFSI (MCS Feedback (MFB) SequenceIdentifier), and an MFB/ASELC (MCS Feedback and Antenna SelectionCommand/Data) field. In some aspects, the frame 900 a includes a veryhigh throughput (VHT) control field instead of the high throughput (HT)control field 904. The VHT control field may include information asdiscussed above with respect to the HT control field 904. In someaspects, the HT-control field 904 or another portion of the frame 900 aincludes information for an STA to determine a rate to transmit CSI.

In the aspect illustrated in FIG. 9B, frame 900 b is illustrated ascomprising the fields 502-516, 902, and 904 illustrated with respect tothe frame 900 a, as well as an additional field. The additional fieldmay comprise a service set identifier that identifies a network, forexample a WLAN. In the illustrated aspect, for example, BSSID field 912comprises a basic service set (BSS) identifier and identifies a BSS. Insome aspects, the BSSID field 912 may be set to a MAC address of an APwhich transmitted the frame 900 b.

The fields 502-516, 902, and 904 illustrated in FIG. 9B may beconfigured as described above with respect to FIG. 9A. In some aspects,one or more of these fields comprise additional or fewer bits thanpreviously described. In some aspects, the BSSID field 912 comprisesanywhere from 1-32 octets. In one aspect, the BSSID field 912 comprises6 octets. In some aspects, the fields 502-516 and 902-912 are arrangedin an order that differs from the order illustrated in FIG. 9A and/orFIG. 9B.

FIG. 10 illustrates another aspect of a frame 1000 including informationfor determining MCS. In the aspect illustrated in FIG. 10, the frame1000 comprises a CSI poll that has been “wrapped” in a control wrapper.Thus, the frame 1000 may be used to request at least a portion of CSIfrom an STA, for example in addition to or in place of the CSI poll 412.

In the illustrated aspect, the frame 1000 may comprise at least one of:a frame control field 1002, a duration field 1004, a destination address(DA) field 1006, a source address (SA) field 1008, a sequence field1012, a remaining segments field 1014, and a Cyclic Redundancy Check(CRC) field 1016.

In the illustrated aspect, the frame control field 1002 comprises 16bits. Also in the illustrated aspect, the duration field 1004 comprises16 bits and may include a length of the frame 1000. The CRC field 1016in the illustrated aspect comprises 32 bits.

In the illustrated aspect, the DA field 1006 comprises 48 bits. The DAfield 1006 may indicate an address of the STA that the frame 1000 isbeing transmitted to, for example as discussed above.

In the illustrated aspect, the SA field 1008 comprises 48 bits. The SAfield 1008 may indicate an address of the AP that is transmitting theframe 1000, for example as discussed above.

In the illustrated aspect, the sequence field 1012 comprises 8 bits. Thesequence field 1012 may comprise information indicative of the sequencenumber common to the CSI feedback for which the AP is requesting anadditional segment. In some aspects, the sequence number indicated bythe sequence field 1012 is the same as or is copied from the sequencenumber for the immediately preceding NDPA frame. Thus, when the frame1000 is used in place of the CSI poll 412 in FIG. 4, the sequence field1012 may have the same value as a CSI sequence field in the NDPA 402,for example.

In the illustrated aspect, the remaining segments field 1014 comprises 8bits. The remaining segments field 1014 indicates the number of segmentsof CSI feedback that the AP expects to receive from the STA addressed bythe DA field 1006. In some aspects, information included with CSIfeedback sent by the STA includes a number of remaining segments left tobe transmitted, as will be discussed below. In these aspects,information in the remaining segments field 1014 may be copied from theremaining segments field of the immediately preceding CSI information.For example, when the AP receives the portion of CSI feedback 408 inFIG. 4, the frame 1000 may be sent to the STA that transmitted theportion of CSI feedback 408 with the remaining segments field 1014having a value of 1. In response, the STA may transmit the one remainingportion of CSI feedback 414.

The frame 1000 may further comprise the carried frame control field 902and the HT-control field 904 described above with respect to FIG. 9A. Asdiscussed above, the HT-control field 904 may comprise informationindicating an MCS or a rate such as a physical layer rate. The STAidentified in the DA field 1006 may use the information in theHT-control field 904 to determine the MCS or rate.

FIG. 11 illustrates an aspect of a CSI report message for communicatingCSI feedback. For example, the CSI report message may be used toimplement the CSI feedback 408 illustrated in FIG. 4. The CSI feedback408 may be determined by a STA in response to a received NDPA frame, forexample the NDPA frame 402 or the NDPA frame 422 described above. Asdescribed in additional detail below, the elements of the CSI feedback408 may be generated based on information in the NDPA frame. The CSIreport message may comprise a frame for communicating the CSI feedback.

In one aspect, the CSI feedback 408 may be generated by one of the STAsidentified in the NDPA frame 402 and autonomously transmitted a SIFSperiod after the NDP frame 404. For example, the first STA identified inan STA information field may generate the CSI feedback 408 andautonomously transmit the CSI feedback 408 to the AP a SIFS period afterreceiving the NDP frame 404. Other STAs identified in the STAinformation field may await a polling message before transmittingrespective CSI feedback, as discussed above.

The CSI feedback 408 may comprise at least one of: a frame control field1102, a duration field 1104, a destination address (DA) field 1106, asource address (SA) field 1108, a CSI feedback control field 1110, a CSIfeedback field 1112 with a computed CSI, or a Cyclic Redundancy Check(CRC) field 1114. The CSI feedback 408 may be of type Action NoAcknowledgement (ACK) message that may not require an ACK response. Inthe illustrated aspect, the CSI feedback 408 may comprise a controlframe.

In some aspects, instead of the field described above, the CSI feedback408 may instead comprise a category field, an action field, a soundingsequence field, the CSI feedback control field 1110, and/or a soundingreport. In such aspects, the CSI feedback 408 may comprise an actionframe. In some aspects, the CSI feedback field 1112 and the soundingreport contain similar information.

In some aspects, channel state information and/or SF may be representedas a matrix, as discussed above, and the sounding report and/or the CSIfeedback field 1112 may comprise the matrix or data indicative thereof.As also discussed above, the matrix comprises a plurality of Eigenmodes, singular vectors, or singular values in some aspects.

There are certain situations in which the STA may determine not to sendfeedback. For example, SF may not be transmitted if a priorcorresponding NDPA/NDP frame was not received, or if the current SF issubstantially similar to a previously transmitted SF. As anotherexample, SF may not be transmitted if the transmission would exceed aPPDU or transmit opportunity (TXOP) limitation. In some aspects, the CSIfeedback field 1112 is omitted in such situations. Thus, the absence ofthe CSI feedback field 1112 may indicate that no SF is being transmittedin some aspects. For example, if a device such as an AP receives the CSIfeedback 408, the device may determine a length of the CSI feedback 408.The length may be used to determine whether the CSI feedback field 1112is included, and it may be determined that no SF will be transmitted ifthe CSI feedback is omitted. In some aspects, an indicator in the CSIfeedback control field 1110 may signify a reason why the SF is not beingtransmitted.

FIGS. 12A-12E illustrate an aspect of a control field for soundingfeedback, for example the CSI feedback control field 1110. In someaspects, the CSI feedback control field 1110 comprises a very highthroughput (VHT) MIMO control field.

In an aspect illustrated in FIG. 12A, CSI feedback control field 1110 amay comprise one or more of an Nc sub-field 1202, an Nr sub-field 1204,a bandwidth sub-field 1206, an Ng sub-field 1212, a codebook sub-field1214, a coefficient sub-field 1216, a remaining segments sub-field 1222,a sequence sub-field 1224, an MU/SU sub-field 1232, a CSI null sub-field1234, an NDPA/NDP not received sub-field 1236, and a difference CSIsub-field 1238. In some aspects, the CSI feedback control field 1110 afurther comprises a reserved sub-field 1242 that includes bits inaddition to those assigned to the sub-fields 1202-1238 that may be usedfor any of a variety of purposes. In some aspects, the sub-fields1202-1242 are arranged in an order that differs from the orderillustrated in FIG. 12.

In the illustrated aspect, the Nc sub-field 1202 comprises at least 3bits. The Nc sub-field 1202 may indicate a number of columns in thematrix discussed above, which represents the CSI for the STA. Using 3bits provides for information regarding at least 5 antennas. In someaspects, the 3 bits provide information for 8 antennas.

In the illustrated aspect, the Nr sub-field 1204 comprises at least 3bits. The Nr sub-field 1204 may indicate a number of rows in the matrixdiscussed above. Using 3 bits provides for information regarding atleast 5 antennas. In some aspects, the 3 bits provide information for 8antennas.

In some aspects, information from the Nss sub-field 704 in the STAinformation 612 is used to determine Nc and Nr. In one aspect, the STAsends SF, for example in the sounding report or the CSI feedback field1112, using exactly the same number of spatial streams (e.g. Eigenmodes) as indicated by the Nss field 704. This may be reflected in Ncand Nr. Using exactly the same number of spatial streams may reduce SFoverhead because the SF size will be no larger than the AP hasdetermined is required. In this way, resources will not be wasted bysending more feedback than requested by the AP. In other aspects, agreater or fewer number of spatial streams may be used by the STA thanare requested by the AP.

In the aspect illustrated in FIG. 12A, the bandwidth sub-field 1206comprises at least 2 bits. The bandwidth sub-field 1206 may indicate abandwidth of the CSI feedback. For example, the 2 bits may be used torepresent four different values (i.e. 0, 1, 2, and 3), each of which maycorrespond to one of the following frequencies: 20 MHz, 40 MHz, 80 MHz,and 160 MHz.

In the aspect illustrated in FIG. 12A, the Ng sub-field 1212 comprisesat least 3 bits. The Ng sub-field 1212 may indicate a grouping of toneson which the STA has generated CSI feedback. Using these three bits, 8different tone group options may be identified. For example, optionsincluding band edge/DC tones may be identified. In some aspects, the Ngsub-field 1212 comprises at least 2 bits.

In some aspects, CSI feedback is generated for each tone being used bythe STA. As an example, there may be up to 468 tones when a bandwidth ofthe CSI feedback is 160 MHz. Some of the tones, however, may be groupedtogether such that information is reported on all of the tones in thegroup concurrently. The Ng sub-field 1212 may indicate how the toneshave been grouped and how many tones are in the group. For example, 3-4tones may be grouped together and the information for these tonesaveraged to generate the CSI feedback.

In one aspect, the STA sends CSI feedback with tone groups that are nolarger than the tone groups indicated by the Ng field 706 in the STAinformation 612. In some aspects, however, the STA may use a smallervalue of Ng than indicated by the Ng field 706. Using groups that are nolarger than indicated by the Ng field 706 will decrease the likelihoodof MU gains being diminished. This decrease may be due to the AP havingdecided the Ng indicated in the Ng field 706 based on an MU/SUtransmission to be used. In other aspects, the STA may use tone groupsthat are larger than the tone groups indicated by the Ng field 706.

In the aspect illustrated in FIG. 12A, the codebook sub-field 1214comprises at least 3 bits. The codebook sub-field 1214 may includeinformation that the AP may use to index into a table indicating how CSIvalues are quantized. In some aspects, the STA quantizes the valuesusing at least as many bits as indicated by the codebook field 714 ofthe STA information 612. Using at least as many bits as indicated by thecodebook field 714 will decrease the likelihood of MU gains beingdiminished. This decrease may be due to the AP having decided arequested quantization based on whether the AP intends to use the SF inan MU or SU protocol. In other aspects, the STA may use fewer bits thanindicated by the codebook field 714. In some aspects, the codebooksub-field 1214 comprises one or more bits.

In the illustrated aspect, the coefficient sub-field 1216 comprises atleast 3 bits. The coefficient sub-field 914 1216 may indicate acoefficient size, which may correspond to a quantization used by the STAfor entries in the matrix described above. In some aspects, thecoefficient sub-field 1216 comprises one or more bits. In some aspects,the coefficient sub-field 1216 is omitted. For example, the SF may beformatted as a compressed feedback, in which case a coefficient size maynot be included.

In some aspects, the STA quantizes entries of the matrix using at leastas many bits as indicated by the coefficient field 712 of the STAinformation 612. Using at least as many bits as indicated by thecoefficient field 712 will decrease the likelihood of MU gains beingdiminished. This decrease may be due to the AP having decided arequested quantization based on whether the AP intends to use the SF forMU or SU. In other aspects, the STA may use fewer bits than indicated bythe coefficient field 712.

In the illustrated aspect, the remaining segments sub-field 1222 maycomprise at least 5 bits. The remaining segments sub-field 1222 mayindicate a number of segments that are yet to be transmitted regardingthe CSI feedback for the STA, as discussed above.

For example, a number of bytes for CSI feedback may be large. Forexample, in the case of 8×3 80MHz uncompressed bandwidth, the number ofbytes for the CSI feedback may be approximately equal to 12K. A largeCSI feedback may not be able to fit into one MAC Protocol Data Unit(MPDU) due to MPDU size limitations. A maximum size of MPDU ofapproximately 8K may be obtained from Aggregated MPDU (A-MPDU) delimiterindication. Furthermore, an MPDU size capability may be even less sinceit is negotiated.

The CSI feedback may be segmented into multiple MPDUs. For example,segments of the CSI feedback may be transmitted within multiple MPDUs ofan A-MPDU. Thus, the remaining segments sub-field 1222 may indicate anumber of remaining segments of the CSI feedback or SF that remains tobe transmitted after the current MPDU.

In the aspect illustrated in FIG. 12A, the sequence sub-field 1224 maycomprise at most 8 bits. The sequence sub-field 924 may compriseinformation indicative of a sequence number that is common among allsegments of a CSI feedback transmitted by the STA. In some aspects, thesequence number indicated by the sequence field 1224 is the same as oris copied from the sequence number from a preceding NDPA frame, forexample from a CSI sequence field.

In the illustrated aspect, the CSI feedback control field 1110 aincludes the MU/SU sub-field 1232 to indicate if the associated CSIfeedback was computed for MU or SU. In some aspects, the CSI feedback isdetermined pursuant to the MU/SU field in an NDPA frame, for example asillustrated in FIG. 7B or 8. In other aspects, the STA determineswhether to compute the CSI for SU or MU. In some aspects, feedbackcalculated for SU may be determined with less resolution. Thus,determining SU feedback instead of MU feedback may reduce processingcomplexity at the STA or may reduce the amount of network resources usedto send the feedback. In the illustrated aspect, the MU/SU fieldcomprises at least 1 bit.

In the illustrated aspect, the CSI null sub-field 1234 comprises atleast 1 bit. The CSI null sub-field 1234 may be used to indicate whetherCSI will be transmitted by the STA. For example, the CSI null sub-field1234 may be set to a value of 0 if no CSI will be transmitted, and maybe set to a value of 1 if CSI will be transmitted. In other aspects,these values may be reversed. In some aspects, the CSI null sub-field1234 may be omitted, and the length of the CSI feedback 408 is used todetermine whether CSI is being transmitted. In such aspects, if it isdetermined that the CSI is not being transmitted, the CSI feedbackcontrol field 1110 a may include an indicator that signifies whether theCSI is not being transmitted because a transmission limitation would beexceeded. For example, the CSI feedback control field 1110 a maycomprise a one bit field indicating whether transmission of the CSIwould exceed a PPDU or TXOP limitation. Exceeding the PPDU or TXOPlimitation may occur if a frame containing the CSI would be too long totransmit, for example.

In the illustrated aspect, the NDPA/NDP not received sub-field 1236comprises at least 1 bit. When the CSI null sub-field 1234 indicatesthat CSI will not be transmitted, the NDPA/NDP not received sub-field1236 may be used to indicate a condition that caused the CSI not to betransmitted. In one aspect, a value of 0 in the NDPA/NDP not receivedsub-field 1236 indicates that a corresponding NDPA frame was notreceived, while a value of 1 in the NDPA/NDP not received sub-field 1236indicates that a corresponding NDP frame was not received.

In another aspect, a single value of the NDPA/NDP not received sub-field1236 is used to indicate that either an NDPA or an NDP corresponding toan identifier in the sequence field 1224 was not received. For example,a value of 0 may be used to indicate this condition. The other value,which in this example is 1, may be used to indicate that no CSI is beingtransmitted because the current CSI is within a threshold of apreviously transmitted CSI. For example, when a last SF stored field ofthe NDPA indicates that the last SF transmitted by the STA has beenstored, the STA may refrain from sending the current SF if the currentSF is substantially similar to the stored SF. In this situation, theNDPA/NDP not received sub-field 1236 may be set to a value to indicatethat the channel has not changed enough to warrant the transmission ofadditional SF.

In the illustrated aspect, the difference CSI sub-field 1238 comprisesat least 1 bit. When the CSI null sub-field 1234 indicates that CSI isbeing transmitted, the difference CSI sub-field may be used to indicatewhether complete CSI is being transmitted or whether informationrepresentative of a difference is being transmitted. For example, avalue of 0 in the difference CSI sub-field 1238 may indicate thatcomplete CSI information is being transmitted. A value of 1 in thedifference CSI sub-field 1238, however, may indicate that informationrepresentative of a difference between a previously transmitted CSI andthe current CSI is being transmitted. For example, when a last SF storedfield of the an NDPA indicates that the last SF of the STA has beenstored at an AP, the STA may calculate and transmit a difference betweenthe current SF and the stored SF, and indicate these actions to the APusing the difference CSI sub-field 1238. As discussed above, thedifference may in some aspects be represented using fewer bits, and maythus reduce overhead.

An AP receiving the CSI feedback control field 1110 a may useinformation therein to determine a CSI. In some aspects, such as theaspects where CSI is not transmitted by the STA as indicated by the CSInull sub-field 1234, the AP may use previously received or stored CSI.In other aspects, the CSI may receive complete CSI from the AP, or mayreceive data representative of a difference and may thereafter calculatecurrent CSI from the difference and a previously stored CSI, for exampleas indicated by the difference CSI sub-field 1238.

In some aspects, the AP may adjust parameters for sending information tothe STA based on information in the CSI feedback control field 1110 a.For example, when the NDPA/NDP not received sub-field 1236 indicatesthat a previously transmitted NDPA or NDP was not received, the AP maytransmit the NDPA or NP again, or may reduce a rate such as a PHY rateused to send future NDPAs and/or NDPs. If the NDPA/NDP not receivedsub-field 1236 indicates that a previously transmitted NDPA and NDP wasreceived, the AP may increase the rate or may adjust another parameterlike a modulation scheme. Further, if the CSI feedback control field1110 a indicates that a channel has not changed or has changed verylittle, for example using the NDPA/NDP not received sub-field 1236and/or the difference CSI sub-field 1238, the AP may decrease thefrequency at which it requests CSI from the STA. Similarly, if the APreceives complete CSI every time or the channel appears to be rapidlychanging, the AP may increase the frequency at which it requests CSIfrom the STA.

In some aspects, one or more of the fields 1202-1242 are omitted fromthe CSI feedback control field 1110. Further, additional fields may beincluded in the CSI feedback control field 1110. In some aspects, someof the bits in the STA information 612 are reserved for other or futureuses. For example, CSI feedback control field 1110 b illustrated in FIG.12B shows an aspect including the Nc sub-field 1202, Nr sub-field 1204,bandwidth sub-field 1206, remaining segments sub-field 1222, sequencenumber sub-field 1224, and optionally the MU/SU sub-field 1232. Inaddition, the CSI feedback control field 1110 b includes an SF nullsub-field 1252 and a use previous SF sub-field 1254.

In the illustrated aspect, the SF null sub-field 1252 comprises at least1 bit. The SF null sub-field 1252 may indicate whether SF is beingtransmitted by the STA. In some aspects, the SF null sub-field isconfigured similar to and/or used similar to the CSI null sub-field1234.

In the illustrated aspect, the use previous SF sub-field 1254 comprisesat least 1 bit. The use previous SF sub-field 1254 may indicate whetherSF previously stored at the AP should be used. For example, when aprevious SF stored field in an NDPA indicates that the previouslytransmitted SF has been stored at the AP, the use previous SF sub-field1254 may be used to indicate that the stored SF should be used as thecurrent SF, or to indicate that the stored SF should be combined with adifference data that is being transmitted by the STA. In some aspects,if the SF null sub-field 1252 and the use previous SF sub-field 1254indicate that no SF is being transmitted, the AP may infer that aprevious NDPA frame and/or NDP frame was not received. Thus, the SF nullsub-field 1252 may indicate that no CSI is being transmitted, while theuse previous SF sub-field 1254 indicates a condition that caused the CSInot to be transmitted, such as channel information being missing or adifference between current SF and previous SF being negligible. A tablesummarizing one aspect of possible values of the SF null sub-field 1252and the use previous SF sub-field 1254 is included below. The tableshows how the values correspond to a potential transmission of CSI.

SF Null Use Prev SF Action 0 0 Regular SF being transmitted 1 0 SF Null(No SF available) 0 1 Difference SF being transmitted 1 1 Use Prev SF(No SF in this frame)

CSI feedback control field 1110 c illustrated in FIG. 12C shows anaspect including the Nc sub-field 1202, Nr sub-field 1204, bandwidthsub-field 1206, remaining segments sub-field 1222, Ng sub-field 1212,codebook sub-field 1214, coefficient sub-field 1216, remaining segmentssub-field 1222, sequence number sub-field 1224, and optionally the MU/SUsub-field 1232 and/or the reserved sub-field 1242. Each of thesesub-fields may be configured as described with respect to FIG. 12A.

In contrast to the CSI feedback control field 1110 a illustrated in FIG.12A, however, the CSI feedback control field 1110 c omits the CSI nullsub-field 1234 and includes instead a first segment sub-field 1262. Inthe illustrated aspect, the first segment sub-field 1262 comprises atleast 1 bit. The first segment sub-field 1262 may be used to indicatewhether CSI feedback that is being transmitted is the first segment ofthat CSI. If an AP receives a CSI segment of a new CSI, but the firstsegment sub-field 1262 does not indicate that the received segment isthe first segment of the new CSI, then the AP may determine that itmissed at least one previously transmitted segment of the new CSI. TheCSI may be identified as new using the sequence number sub-field 1224and/or using the remaining segments sub-field 1222. For example, if theremaining segments sub-field 1222 associated with a previous CSI segmentindicated that the segment was the last segment, any CSI segments thatare received in the future may be determined to be associated with newCSI.

Further, the NDPA/NDP not received sub-field 1236 and the difference CSIsub-field 1238 illustrated in FIG. 12A have been replaced with a singleCSI null and difference sub-field 1264 in the CSI feedback control field1110 c. In the illustrated aspect, the CSI null and difference sub-field1264 comprises at least 2 bits. Implementing the CSI null and differencesub-field 1264 in this way allows the CSI feedback control field 1110 cto be implemented using the same number of bits as the CSI feedbackcontrol field 1110 a. The CSI null and difference sub-field 1264 mayindicate whether regular SF is being transmitted, whether a differencebetween current SF and previous SF is negligible, and/or whether SF isnot available. In one aspect, SF may not be available if a correspondingNDP or NDPA frame was not received. Those of skill in the art willappreciate that the CSI null and difference sub-field 1264 may be usedto indicate the same or similar information as indicated by one or moreof the CSI null sub-field 1234, NDPA/NDP not received sub-field 1236,difference CSI sub-field 1238, SF null sub-field 1252, and use previousSF sub-field 1254. One aspect of possible values of the CSI null anddifference sub-field 1264 is summarized in the table below. The tableillustrates how the values correspond to a potential transmission ofCSI.

CSI null and difference sub-field Action 0 0 Regular feedback 0 1 SF notavailable: may be set if NDPA or NDP frame was not received 1 0 Zerodifference indicates that NDPA or NDP frame was received, but no CSIneeds to be sent 1 1 Reserved, or indicates that the CSI feedback is adifference CSI

Those of skill in the art that other values or combinations of valuesmay correspond to the listed actions. For example, the actionsassociated with “0 1” and “1 1” may be transposed in the table above.

In the table above, values of “1 1” may be used to indicate that CSIfeedback being transmitted is a difference CSI. In other aspects, thevalues of “1 1” may be reserved. In some aspects, the values of “1 1”may be used to indicate that CSI is not being included becausetransmission of the CSI feedback would exceed a transmission limitation,such as a PPDU or a TXOP limitation. For example, if a length of CSIfeedback, such as the CSI Feedback 408, indicates that no SF is beingtransmitted, the values of “1 1” may indicate that the condition thatcaused the non-transmission is a PPDU or TXOP limitation.

In some aspects, if the length of the CSI Feedback 408 indicates that noSF is being transmitted, one or more of the indicators or sub-fieldsdiscussed above may be used to indicate a condition that caused the SFnot to be transmitted. For example, the NDPA/NDP not received sub-field1236, difference CSI sub-field 1238, use previous SF sub-field 1254,and/or the CSI null and difference sub-field 1264 may signify what thecondition is. In other aspects, a new field may be defined to indicatethe condition. In still other aspects, one or more bits that would beused for another purpose when CSI is being transmitted can be used toprovide this indication. For example, one or more of the bits in theremaining segments field 1222 may be used to indicate the condition if alength of the CSI Feedback 408 indicates that SF is not beingtransmitted.

CSI feedback control field 1110 d illustrated in FIG. 12D shows anaspect including the Nc sub-field 1202, Nr sub-field 1204, bandwidthsub-field 1206, Ng sub-field 1212, codebook sub-field 1214, sequencenumber sub-field 1224, and the MU/SU sub-field 1232. In the illustratedaspect, however, the bandwidth sub-field 1206 is illustrated as achannel width sub-field. Further, the Ng sub-field 1212 is illustratedas a grouping sub-field. Additionally, the MU/SU sub-field 1232 isillustrated as a feedback type sub-field, and the sequence numbersub-field 1224 is illustrated as a sounding sequence sub-field. Each ofthese sub-fields may be configured as described with respect to FIG.12A.

The CSI feedback control field 1110 d further includes the reservedsub-field 1242. In the aspect illustrated in FIG. 12D, the reservedsub-field 1242 may be used to indicate whether CSI will be transmitted.Thus, the reserved sub-field 1242 may indicate that the frame of CSIfeedback 408 is a null feedback frame, for example omitting informationfrom the CSI feedback field 1112 or wholly omitting the CSI feedbackfield 1112. The reserved sub-field 1242 may therefore be used in someaspects to indicate information similar to the CSI null sub-field 1234discussed above.

In the aspect illustrated in FIG. 12D, the reserved sub-field 1242 mayinstead or additionally be used to indicate whether CSI feedback that isbeing transmitted is the first segment of that CSI. The reservedsub-field 1242 may therefore be used in some aspects to indicateinformation similar to the first segment sub-field 1262 discussed above.

In the aspect illustrated in FIG. 12D, the reserved sub-field 1242 mayinstead or additionally be used to indicate a number of remainingsegments of the CSI feedback or SF that remains to be transmitted afterthe current MPDU. The reserved sub-field 1242 may therefore be used insome aspects to indicate information similar to the remaining segmentssub-field 1222 discussed above. Thus, the reserved sub-field 1242 mayindicate which one of a plurality of feedback segments is first and howmany segments of the feedback are missing. Indicating first andremaining segments may alert a receiver, such as an AP, of how manysegments to expect and whether the segments have all been received.

In the aspect shown in FIG. 12D, the reserved sub-field 1242 isillustrated as comprising four bits. In one aspect, one of the four bitsmay be used to indicate whether a segment of feedback being transmittedis a first segment. For example, a bit value of “1” may be used toindicate that the segment is a first segment, and a bit value of “0” mayindicate that the segment is not a first segment. In some aspects, B15is used as the one bit.

In such aspects, one or more of the remaining bits in the reservedsub-field 1242 may be used to indicate a number of segments remaining tobe transmitted. For example, if bit B15 is used to indicate whether thesegment being transmitted is a first segment, bits B12-B14 may be usedto indicate the number of remaining segments. A value of “111” mayindicate that seven segments are remaining, a value of “110” mayindicate that six segments are remaining, and so on. If a single segmentis being transmitted, the first segment bit may be set to “1” and theremaining segments bits all set to “0.” If B12-B14 indicate the numberof remaining segments and B15 indicates whether the segment is a firstsegment, the reserved sub-field 1242 may therefore have a value of“0001” to indicate that a single segment of feedback is beingtransmitted.

In some aspects, feedback may be split into no more than eight segments.In these aspects, there can be at most seven segments remaining Sevensegments may be remaining, however, only if the segment beingtransmitted is the first segment. Thus, there would be no circumstancein which a segment that is not the first segment would indicate thatseven segments are remaining In such aspects, the first segment bit maybe set to “0” and the remaining segments bits all set to “1” to indicatethat CSI is not being transmitted. If B12-B14 indicate the number ofremaining segments and B15 indicates whether the segment is a firstsegment, the reserved sub-field 1242 may therefore have a value of“1110” to indicate that a null feedback frame is being transmitted.Thus, an indication that a first segment is not being transmitted incombination with an indication that the maximum number of remainingsegments have yet to be transmitted may alert a receiver, such as an AP,that no CSI is being transmitted.

In some aspects, if the reserved sub-field 1242 indicates that no CSI isbeing transmitted, all of the bits preceding the reserved sub-field 1242may be used as reserved bits. Thus, if a null feedback frame istransmitted, bits B0-B11 may be reserved. In some aspects, one or moreof these bits may be used to indicate a condition that caused the CSInot to be transmitted.

For example, bits B10-B11 may be used to a reason that feedback ismissing. The reason may relate to the reception of sounding information,a transmission limitation, or calculated CSI, among other reasons. Insome aspects, B10-B11 are set to a value of “00” if sounding informationis missing, for example if an NDPA or NDP frame was not received or wasreceived incorrectly. In some aspects, B10-B11 are set to a value of“01” if feedback cannot be sent due to a TXOP limitation. In someaspects, B10-B11 are set to a value of “10” if feedback cannot be sentdue to a PPDU limitation. In some aspects, B10-B11 are set to a value of“11” if previously transmitted channel state information issubstantially similar to current channel state information. In someaspects, the value of “11” is reserved for B10-B11.

In the aspect illustrated in FIG. 12D, the coefficient size sub-field isomitted. Further, the MU/SU sub-field 1232 is disposed before anyremaining segments, first segment, and null feedback information orindicators. Additionally, the sequence number sub-field 1224 is disposedafter such information or indicators, and therefore after the reservedfield 1242.

FIG. 12E illustrates an aspect of CSI feedback control field 1110 eshowing the reserved sub-field 1242 being split into a remainingsegments sub-field 1272 and a first segment sub-field 1274. In theillustrated aspect, the remaining segments sub-field 1272 comprises bitsB12-B14 of the field 1110 e and the first segment sub-field 1274comprise bit B15 of the field 1110 e. The remaining segments sub-field1272 may be used to convey similar information or configured similar tothe remaining segments sub-field 1222 discussed above. The first segmentsub-field 1274 may be used to convey similar information or configuredsimilar to the first segment sub-field 1262 discussed above. Whenconsidered together, the remaining segments sub-field 1272 and the firstsegment sub-field 1274 may be used to convey similar information as theCSI null sub-field 1234 and/or the SF null sub-field 1252 discussedabove.

The remaining segments sub-field 1272 and the first segment sub-field1274 may be set to various values as described above with respect tobits B12-B14 and B15, respectively, to indicate information about CSIfeedback. Example values of these sub-fields, as well as the remainingsub-fields 1202-1232 of the field 1110 e, are enumerated in the tablebelow. The values below are only illustrative, and are not intended tobe limiting. One having ordinary skill in the art will appreciate thatother values may be used or other information may be indicated by theillustrated values.

Sub-field Values and Description of Indicated Information Nc IndexIndicates the number of columns in a matrix minus one: Set to 0 for Nc =1 Set to 1 for Nc = 2 . . . Set to 7 for Nc = 8 Nr Index Indicates thenumber of rows in a matrix minus one: Set to 0 for Nr = 1 Set to 1 forNr = 2 . . . Set to 7 for Nr = 8 Channel Indicates the width of thechannel in which a measurement Width was made: Set to 0 for 20 MHz Setto 1 for 40 MHz Set to 2 for 80 MHz Set to 3 for 160 MHz or 80 + 80 MHzGrouping Number of carriers grouped into one: Set to 0 for Ng = 1 (Nogrouping) Set to 1 for Ng = 2 Set to 2 for Ng = 4 The value 3 isreserved Feedback Set to 0 if the feedback report is for SU-BF. If it isset to 0, Type the feedback report frame shall not include the MUExclusive Beamforming Report field. Set to 1 if the feedback report isfor MU-BF. If it is set to 1, the feedback report frame shall includethe MU Exclusive Beamforming Report field Codebook Indicates the size ofcodebook entries: Information If Feedback Type is set to 0 (SU-BF) Setto 0 for 2 bit for ψ, 4 bits for φ Set to 1 for 4 bit for ψ, 6 bits forφ If Feedback Type is set to 1 (MU-BF) Set to 0 for 5 bit for ψ, 7 bitsfor φ Set to 1 for 7 bit for ψ, 9 bits for φ Remaining Contains theremaining segment number for the associated segments measurement report.Valid range: 0 to 7. Set to 0 for the last segment of a segmented reportor the only segment of an unsegmented report. When First segment is setto 0, Remaining segments equal to 7 indicates the frame is a NullFeedback frame, e.g. the VHT Compressed Beamforming Report and MUExclusive Beamforming Report fields are not present. First Set to 1 ifthe segment is the first. Set to 0 if the segment segment is the onlysegment. Sounding Sequence number from the NDPA soliciting feedback.Sequence

FIG. 13 illustrates an aspect of an access point (AP) 1300 for usewithin the system 100. The AP 1300 may comprise the AP 110 illustratedin FIG. 1 or FIG. 2. As discussed above, the AP 1300 may be implementedas a wireless device, for example as a wireless device 302 illustratedin FIG. 3. The AP 1300 may be used to communicate with a user terminalor STA as described above with respect to FIGS. 4-12.

The AP 1300 may comprise an NDPA module 1302 for generating an NDPAframe, for example the NDPA frame 402 or 422. When generating an NDPAframe, the NDPA module 1202 may determine whether SF was received froman STA in response to a previous NDPA frame or in response to a pollingmessage. The SF may be received by a receiving module 1204, for example,and the NDPA frame may have been transmitted by a transmitting module1206. The polling message may be generated by a polling module 1208. Theresult of this determination may be included in the NDPA frame, forexample in a last SF received field as discussed above.

The NDPA module 1302 may further determine whether the last SF polledfor by the polling module 1308 was stored, for example stored in amemory 1312. The result of this determination may be included in theNDPA frame, for example in a last SF stored field or a previous SFstored field as discussed above.

In some aspects, the NDPA module 1302 is configured to wrap an NDPAframe in a control wrapper, for example as shown in FIG. 9A or FIG. 9B.In these aspects, the NDPA module 1302 may be configured to determine anHT-control field and/or MCS for an STA to send requested CSI. The NDPAmodule 1302 may also determine a rate at which the STA should use tosend the requested CSI. The result of this determination may be includedin the wrapped NDPA frame.

The NDPA module 1202 may be configured to determine one or more STAsfrom which CSI feedback information is being requested. Informationidentifying these STAs may be included in an STA information field, asdescribed above with respect to FIGS. 6A-6C.

The NDPA module 1302 may be configured to determine parameters for eachof the STAs to use for reporting CSI feedback. For example, the NDPAmodule 1202 may determine whether each STA or all of the STAscollectively should compute CSI for SU or MU. The NDPA module 1302 mayfurther be configured to determine a number of spatial channels orstreams (e.g., Eigen modes) of CSI feedback to be computed at the STAs,a grouping of tones on which the STAs are to generate CSI feedback, acoefficient size corresponding to a quantization used by the STAs formatrix entries of the CSI feedback, and/or codebook informationindicating a quantization for angles that the STAs should use for CSIfeedback, as described above with respect to FIG. 7. In some aspects,the NDPA module 1302 is configured to determine one or more of the aboveparameters based on whether the CSI feedback will be used for MU or SU.

In some aspects, the NDPA module 1302 is configured to determine afrequency for sending NDPA frames, for example based at least in part onCSI or changing channel conditions indicated in CSI feedback, asdiscussed above. The NDPA module 1302 may further be configured togenerate or determine any of the other information described above withrespect to the NDPA frame 422. In some aspects, functionality of theNDPA module 1302 is implemented using at least the controller 230illustrated in FIG. 2.

The receiving module 1304 may be used to receive control information,CSI feedback, and/or other communications from an STA such ascommunications indicating that no CSI feedback will be transmitted fromthe STA. The received data may be demodulated, downconverted, orotherwise processed by the receiving module 1304 or another module. Thereceiving module 1304 may be implemented using a receiver, for examplethe receiver 312 illustrated in FIG. 3, or a combination of receivers,for example the receivers 222 a-222 ap illustrated in FIG. 2. Thereceiving module 1304 may be implemented in a transceiver, and maycomprise a demodulator and/or a receive data processor, for example theRX data processor 242. In some aspects, the receiving module 1304comprises an antenna and a transceiver, for example the antenna 224 andthe transceiver 222. The transceiver may be configured to demodulateinbound wireless messages. The messages may be received via the antenna.

The transmitting module 1306 may be used to transmit NDPA frames and/orpolling messages. In some aspects, the transmitting module 1306 isconfigured to wirelessly transmit the NDPA frame, for example to theuser terminal 120. The transmitting module 1306 may be implemented usinga transmitter, for example the transmitter 310 illustrated in FIG. 3, ora combination of transmitters, for example the transmitters 222 a-222 apillustrated in FIG. 2. The transmitting module 1306 may be implementedin a transceiver, and may comprise a modulator and/or a transmissiondata processor, for example the TX data processor 210. In some aspects,the transmitting module 1306 comprises an antenna and a transceiver, forexample the antenna 224 and the transceiver 222. The transceiver may beconfigured to modulate outbound wireless messages going to a userterminal or STA. The messages may be transmitted via the antenna.

The polling module 1308 may be used to generate polling messages totransmit to the STAs, for example any of the CSI polls 412, 416. Thepolling module may determine which STA to transmit a polling messagebased on information received via the receiving module 1304. Forexample, remaining segment information received in a control message orfield via the receiving module 1304 may be used by the polling module1308 to generate a polling message.

In some aspects, the polling module 1308 is configured wrap a pollingmessage in a control wrapper, for example as shown in FIG. 10. In theseaspects, the polling module 1308 may be configured to determine anHT-control field and/or MCS for an STA to send requested CSI. The resultof this determination may be included in the wrapped polling message.

The polling module 1308 may further be configured to generate ordetermine any of the other information described above with respect topolling messages such as the CSI poll 412 or the CSI poll 416, or theframe 1000, for example to include the sequence number of an NDPA frame.In some aspects, functionality of the polling module 1308 is implementedusing at least the controller 230 and/or the scheduler 234 illustratedin FIG. 2.

The memory 1312 may be configured to store CSI information received fromone or more STAs, for example via the receiving module 1304. Asdescribed above, the CSI may be represented as a matrix, which may bestored in the memory 1312. Other formats for representing the CSI mayadditionally be stored in the memory 1312. In some aspects, CSI that hastimed out or expired may be periodically deleted from the memory 1312.The memory 1312 may be volatile or non-volatile, or may be a combinationof both. In some aspects, functionality of the memory 1312 isimplemented using at least the memory 232 illustrated in FIG. 2 or thememory 306 illustrated in FIG. 3.

The AP 1300 may further comprise CSI processing module 1314 forprocessing received CSI feedback, for example received using thereceiving module 1304. The CSI processing module 1314 may be configuredto process the CSI feedback using one or more of the parametersindicated in a received message, for example according to SU or MU. TheCSI processing module 1314 may also be configured to process the CSIfeedback using one or more of the parameters indicated in a previouslytransmitted frame, for example using the MCS transmitted in a wrappedframe.

In some aspects, the CSI processing module 1314 is configured todetermine if a communication is received from an STA indicating that theSTA has no CSI feedback to transmit. For example, a CSI null field maybe received in a CSI feedback indicating that no CSI will be received orone or more values in a reserved field, such as a first segments fieldand a remaining segments field, may indicate that no CSI will bereceived. The CSI processing module may be configured to determine ifpreviously stored CSI should be used, for example by evaluating an SFnull field and a use previous SF field. In some aspects, the CSIprocessing field is configured to change a rate or modulation fortransmitting CSI requests based on information received in the CSIfeedback, as described above. In some aspects, the CSI processing module1314 may determine that no CSI will be received based on a length of thecommunication. The CSI processing module 1314 may also be configured todetermine a condition that caused the CSI not to be received.

In some aspects, the CSI processing module 1314 is configured togenerate CSI from a difference received in a CSI feedback. For example,when a difference CSI field or use previous SF field indicates that datarepresentative of a difference between current CSI and a previouslystored CSI is being transmitted, the CSI processing module 1314 maydetermine the current CSI using the difference data and CSI stored inthe memory 1312.

In some aspects, the CSI processing module 1314 is configured to analyzereceived CSI feedback to determine a frequency for sending NDPA frames,for example based at least in part on CSI or changing channel conditionsindicated in CSI feedback. This information may be communicated to theNDPA module 1302. In some aspects, functionality of the CSI processingmodule 1210 is implemented using at least the controller 230 and/or theRX data processor 242 illustrated in FIG. 2.

Those of skill in the art will appreciate various circuits, chips,modules, and/or components, which may comprise either software orhardware or both, that may be used to implement the modules describedabove with respect to the AP 1300. One or more of the modules of the AP1300 may be partially or wholly implemented in the processor 304illustrated in FIG. 3.

FIG. 14 illustrates an aspect 1400 of a method for communication. Themethod may be implemented by the AP 1200, for example, to requestchannel state information from an STA and to optionally inform the STAof whether past SF has been received from the STA and/or stored at theAP. Although the method below will be described with respect to elementsof the AP 1200, those of skill in the art will appreciate that othercomponents may be used to implement one or more of the steps describedherein.

At step 1402, a first request for channel state information istransmitted, for example using the transmitting module 1204. The firstrequest may comprise a null data packet announcement or a pollingmessage, for example. The NDPA module 1302 or the polling module 1308may be used to generate the request.

Proceeding to step 1404, it is determined whether the channel stateinformation has been received in response to the first request orwhether the channel state information has been stored subsequent to thetransmission. This determination may be performed by the CSI processingmodule 1314, for example. The channel state information may be receivedat the receiving module 1304, or may be stored in the memory 1312.

Moving to step 1406, a second request comprising an indicator signifyinga result of the determination is transmitted, for example using thetransmitting module 1306. The second request may comprise an NDPA frame,for example. In some aspects, the result of the determination isindicated in a last SF received field, a last SF stored field, or aprevious SF stored field, as discussed above with respect to FIG. 7. TheNDPA module 1302 and/or the CSI processing module 1314 may be used increating the second request.

FIG. 15 illustrates an aspect 1500 of a method for communication. Themethod may be implemented by the AP 1200, for example, to receive datarepresentative of a portion of channel state information, or to receivenotice that the channel state information will not be transmitted. Insome aspects, the method 1500 may be used to determine why channel stateinformation is not being transmitted from an STA. Although the methodbelow will be described with respect to elements of the AP 1200, thoseof skill in the art will appreciate that other components may be used toimplement one or more of the steps described herein.

At step 1502, a request for channel state information is transmitted,for example by the transmitting module 1306. Thereafter, at step 1504, acommunication is received. The communication may comprise a firstindicator and a second indicator signifying whether the channel stateinformation is included in the communication. If the first indicatorand/or the second indicator signifies that the channel state informationis included, the first indicator and/or the second indicator furthersignifies whether the channel state information comprises informationrepresentative of a difference between current channel state informationand previously received channel state information. The first and secondindicators may comprise two or more of a CSI null field, a NDPA/NDP notreceived field, an SF null field, a use previous SF field, and/or a CSInull and difference field, as described above with respect to FIG. 12.The communication may be received using the receiving module 1304, forexample. The communication may be processed by the CSI processing module1314, for example, to determine if CSI information is included and/or todetermine whether CSI stored at the AP will be used.

FIG. 16 illustrates an aspect 1600 of a method for communication. Themethod may be implemented by the AP 1200, for example, to notify an STAof MCS for transmitting CSI. Although the method below will be describedwith respect to elements of the AP 1200, those of skill in the art willappreciate that other components may be used to implement one or more ofthe steps described herein.

At step 1602, a modulation coding scheme (MCS) or a rate for receivingchannel state information is determined. In some aspects, the NDPAmodule 1302 may perform the determination. In other aspects, the pollingmodule 1308 may determine perform the determination. In some aspects,the CSI processing module 1312 may be configured to perform a portion orall of the determination, for example based on communications receivedfrom an STA such as whether a state of a channel has been changing. Thecommunications may be received using the receiving module 1304, forexample.

Next, at step 1604, a wrapper frame is transmitted. The wrapper framemay comprise a control field indicating the determined MCS or rate andat least one field indicating that at least a portion of the channelstate information is requested. The wrapper frame may comprise a wrappedNDPA frame, as discussed above with respect to FIG. 9A, or a wrappedpolling message, as described above with respect to FIG. 10. The wrapperframe may be transmitted by the transmitting module 1306, for example.

FIG. 17 illustrates an aspect of a station (STA) 1700 for use within thesystem 100. The STA 1700 may comprise any of the user terminals 120illustrated in FIG. 1 or FIG. 2. As discussed above, the STA 1700 may beimplemented as a wireless device, for example as a wireless device 302illustrated in FIG. 3. The STA 1700 may be used to communicate with anAP as described above with respect to FIGS. 4-12.

The STA 1700 may comprise a receiving module 1702 for receiving an NDPAframe and/or a CSI poll. For example, the receiving module 1702 may beconfigured to receive the NDPA frame 402 or 422 and/or either of the CSIpolls 412, 416. Further, the receiving module 1702 may be configured toreceive an NDP frame and frames that comprise wrapped NDPA frames orwrapped polling messages. Received data may be demodulated,downconverted, or otherwise processed by the receiving module 1702 oranother module. The receiving module 1702 may be implemented using areceiver, for example the receiver 312 illustrated in FIG. 3, or acombination of receivers, for example the receivers 254 m-254 mu or 254xa-254 xu illustrated in FIG. 2. The receiving module 1702 may beimplemented in a transceiver, and may comprise a demodulator and/or areceive data processor, for example the RX data processor 270. In someaspects, the receiving module 1702 comprises an antenna and atransceiver, for example the antenna 252 and the transceiver 254. Thetransceiver may be configured to demodulate inbound wireless messages.The messages may be received via the antenna.

The STA 1700 may further comprise a CSI feedback module 1704 fordetermining CSI feedback. The CSI feedback module 1704 may be configuredto determine the CSI feedback based on a received NDP frame associatedwith a received NDPA frame. The CSI may be represented as a matrix, asdiscussed above. Parameters of the CSI feedback may be determined insome aspects by the CSI feedback module 1704. In some aspects, the CSIfeedback module is configured to determine MCS from a communication suchas a control wrapper received via the receiving module 1702. Forexample, the CSI feedback module may determine MCS for CSI from anHT-control field included in a wrapped NDPA frame, as described abovewith respect to FIG. 9A.

The CSI feedback module 1704 may be configured to determine whether tocompute regular/complete CSI, or whether to compute a difference betweena previous CSI and current CSI. For example, the CSI feedback module1704 may evaluate a last SF stored field or a previous SF stored fieldin an NDPA, as well as conditions of a channel, as discussed above. If acondition of the channel is substantially similar to a condition when aprevious SF was stored, the CSI feedback module 1704 may determine notto send any CSI. In some aspects, the CSI feedback module 1704 maydetermine that SF has been stored at an AP, and may compute differencedata to send to the AP to calculate current SF. The determinations ofthe CSI feedback module 1704 may be included in CSI feedback, forexample in the CSI feedback 408 illustrated in FIGS. 11 and 12. In someaspects, the determinations may be indicated by a CSI null field, adifference CSI field, an SF null field, a use previous SF field, a CSInull and difference field, and/or one or more values in a reserved fieldsuch as a first segments field and a remaining segments field. A reasonthat caused the CSI feedback module 1704 not to send CSI may beindicated by an NDPA/NDP not received field, a difference CSI field, anSF null field, a use previous SF field, a CSI null and difference field,and/or in fields that become reserved once it is determined that no CSIwill not be transmitted, for example in a CSI feedback communicationtransmitted to the AP. In some aspects, the CSI feedback module 1704 isconfigured to generate a CSI feedback communication having a length thatindicates that the CSI will not be transmitted. In some aspects, the CSIfeedback module 1704 may determine that CSI feedback will not betransmitted due to a transmission limitation, such as a PPDU or TXOPlimitation.

The CSI feedback module 1704 may further be configured to generate ordetermine any of the other information described above with respect tothe CSI feedback 408. In some aspects, functionality of the CSI feedbackmodule 1704 is implemented using at least the controller 280 and/or thechannel estimator 278. In some aspects, the CSI feedback module 1704comprises a quantizer to quantize angles and/or entries in a matrixrepresenting the CSI.

The STA 1700 may further comprise a rate adjustment module 1706 fordetermining an adjustment of a rate used to the send the CSI feedbackdetermined by the CSI feedback module 1704. For example, the rateadjustment module 1706 may increase a PHY rate for sending the CSIfeedback when a last SF received field in one or more received NDPAframes indicates that the CSI feedback that the STA 1700 has beentransmitting has been successfully received. Similarly, the rateadjustment module 1706 may decrease a rate such as a PHY rate if a lastSF received field, a last SF stored field, or a previous SF stored fieldindicates that a previously transmitted SF was not received or could notbe stored. In some aspects, the rate adjustment module 1706 may adjustother parameters of the CSI feedback, for example a modulation of theCSI feedback. The rate adjustment module 1706 may determine or adjust arate based on a control field in a wrapper, as discussed above. The rateadjustment module 1706 may also be configured to determine a rate atwhich a message, for example a polling message, is received, for exampleat the receiving module 1702.

The rate adjustment module 1706 may be configured to perform any of therate adjustment procedures described above with respect to FIG. 7. Insome aspects, functionality of the rate adjustment module 1706 isimplemented using at least the controller 280. In some aspects, the rateadjustment module 1706 looks up values or parameters in a memory, suchas the memory 282, for example to determine an appropriate rate oradjustment.

The STA 1700 further comprises a transmitting module 1708 may fortransmitting CSI feedback. For example, the transmitting module 1708 maybe configured to transmit the CSI feedback determined by the CSIfeedback module 1704. The transmitting module may be configured totransmit at a rate determined by the rate adjustment module 1706 orusing another parameter determined by the rate adjustment module 1706.In some aspects, the transmitting module 1708 is configured towirelessly transmit the CSI feedback, for example to the AP 110. Thetransmitting module 1708 may be implemented using a transmitter, forexample the transmitter 310 illustrated in FIG. 3, or a combination oftransmitters, for example the transmitters 254 m-254 mu or 254 xa-254 xuillustrated in FIG. 2. The transmitting module 1708 may be implementedin a transceiver, and may comprise a modulator and/or a transmissiondata processor, for example the TX data processor 288. In some aspects,the transmitting module 1708 comprises an antenna and a transceiver, forexample the antenna 252 and the transceiver 254. The transceiver may beconfigured to modulate outbound wireless messages going to an AP. Themessages may be transmitted via the antenna.

Those of skill in the art will appreciate various circuits, chips,modules, and/or components, which may comprise either software orhardware or both, that may be used to implement the modules describedabove with respect to the STA 1700. One or more of the modules of theSTA 1700 may be partially or wholly implemented in the processor 304illustrated in FIG. 3.

Although described separately, it is to be appreciated that functionalblocks described with respect to the AP 1300 and the STA 1700 need notbe separate structural elements. Similarly, one or more of thefunctional blocks or portions of the functionality of various blocks maybe embodied in a single chip. Alternatively, the functionality of aparticular block may be implemented on two or more chips. In addition,additional modules or functionality may be implemented in the AP 1300and the STA 1700. Similarly, fewer modules or functionalities may beimplemented in the AP 1300 and the STA 1700, and the components of theAP 1300 and/or the STA 1700 may be arranged in any of a plurality ofconfigurations. Additional or fewer couplings between the variousmodules illustrated in FIGS. 2, 3, 13 and 17 or between additionalmodules may be implemented.

FIG. 18 illustrates an aspect 1800 of a method for communication. Themethod may be implemented by the STA 1700, for example, to determinewhether transmitted SF has been received and/or stored at an AP.Although the method below will be described with respect to elements ofthe STA 1700, those of skill in the art will appreciate that othercomponents may be used to implement one or more of the steps describedherein.

At step 1802, a first request for channel state information is received,for example using the receiving module 1702. The first request maycomprise a null data packet announcement or a polling message, forexample.

At step 1804, a frame comprising the channel state information istransmitted. The channel state information may be determined using theCSI feedback module 1704, for example, and may be transmitted using thetransmitting module 1708, for example. The CSI feedback may bedetermined using the first request received at step 1802.

Proceeding to step 1806, a second request is received. The secondrequest comprises a first indicator signifying whether the channel stateinformation has been received in response to the first request orwhether the channel state information has been stored subsequent to thetransmission. The second request may be received using the receivingmodule 1702, for example. The second request may comprise an NDPA frame.In some aspects, the second request is processed by the CSI feedbackmodule 1704 and/or the rate adjustment module 1706 to determine whetherto send CSI feedback or to adjust a parameter such as a rate used tosend the CSI.

FIG. 19 illustrates an aspect 1900 of a method for communication. Themethod may be implemented by the STA 1700, for example, to determinewhether to transmit CSI, and in some aspects to indicate to an APwhether transmitted CSI comprises a difference CSI. Although the methodbelow will be described with respect to elements of the STA 1700, thoseof skill in the art will appreciate that other components may be used toimplement one or more of the steps described herein.

At step 1902, a message indicating that channel state information isrequested is received, for example using the receiving module 1702. Insome aspects, the message comprises an NDPA frame or a polling message.The message may indicate whether previously transmitted SF is stored atan AP.

Thereafter, at step 1904 it is determined whether to transmit thechannel state information. The determination may be performed by the CSIfeedback module 1704, for example. The CSI feedback module 1704 mayevaluate whether a channel condition has changed, and whether CSI isstored at the AP, for example as described above.

Moving to step 1906, a communication is transmitted. The communicationmay comprise a first indicator and a second indicator signifying aresult of the determination. If the first indicator and/or the secondindicator signifies that the channel state information will betransmitted, the first indicator and/or the second indicator may signifywhether the channel state information comprises informationrepresentative of a difference between current channel state informationand previously transmitted channel state information. The firstindicator may comprise a CSI null field, an SF null field, and/or aportion of a CSI null and difference field, for example. The secondindicator may comprise a difference CSI field, a use previous SF field,and/or a portion of a CSI null and difference field, for example. Theindicators may be determined by the CSI feedback module 1704, forexample. The communication may comprise CSI feedback, for example theCSI feedback 408, or another communication indicating whether CSI willbe transmitted. The communication may be transmitted using thetransmitting module 1708, for example.

FIG. 20 illustrates an aspect 2000 of a method for communication. Themethod may be implemented by the STA 1700, for example, to determine MCSfor transmitting CSI. Although the method below will be described withrespect to elements of the STA 1700, those of skill in the art willappreciate that other components may be used to implement one or more ofthe steps described herein.

At step 2002, a wrapper frame is received, for example using thereceiving module 1702. The wrapper frame may comprise a control fieldindicating a modulation coding scheme (MCS) for transmitting channelstate information, and at least one field indicating that at least aportion of channel state information is requested. The wrapper frame maycomprise a wrapped NDPA frame, as discussed above with respect to FIG.9A, or a wrapped polling message, as described above with respect toFIG. 10

Subsequently, at step 2004, at least the portion of the channel stateinformation requested by the frame is transmitted, for example using thetransmitting module 1708. The CSI feedback module 1704 and/or the rateadjustment module may extract MCS from the control field in the receivedwrapper frame to determine how to send the CSI. The channel stateinformation may be transmitted as CSI feedback such as the CSI feedback408. The channel state information may be determined by the CSI feedbackmodule 1704, for example as described above.

FIG. 21 illustrates an aspect 2100 of a method for communication. Themethod may be implemented by the AP 1200, for example, to determine thatchannel state information will not be received, and to determine why thechannel state information is not being transmitted from an STA. Althoughthe method below will be described with respect to elements of the AP1200, those of skill in the art will appreciate that other componentsmay be used to implement one or more of the steps described herein.

At step 2102, a request for channel state information is transmitted,for example by the transmitting module 1306. Thereafter, at step 2104, acommunication is received. The communication may comprise an indicator.The communication may be received using the receiving module 1304, forexample.

After reception of the communication, it is determined that thecommunication does not include channel state information based on alength of the communication at step 2106. Further, at step 2108, acondition that caused the channel state information not to be receivedis determined based on a value of the indicator. The indicator maycomprise a NDPA/NDP not received field, a use previous SF field, and/ora CSI null and difference field, as described above with respect to FIG.12. The indicator may further comprise a bit, field, or other signifierindicative of whether a transmission limitation would be exceeded bytransmitting the channel state information. The determining at step the2106 and/or at the step 2108 may be performed by the CSI processingmodule 1314, for example.

FIG. 22 illustrates an aspect 2200 of a method for communication. Themethod may be implemented by the STA 1700, for example, to determinewhether to transmit CSI, and to indicate to an AP a reason why CSI isn'tbeing transmitted. Although the method below will be described withrespect to elements of the STA 1700, those of skill in the art willappreciate that other components may be used to implement one or more ofthe steps described herein.

At step 2202, a message indicating that channel state information isrequested is received, for example using the receiving module 1702. Insome aspects, the message comprises an NDPA frame or a polling message.The message may indicate whether previously transmitted SF is stored atan AP.

Thereafter, at step 2204 it is determined not to transmit the channelstate information. The determination may be performed by the CSIfeedback module 1704, for example. The CSI feedback module 1704 mayevaluate whether a channel condition has changed, whether CSI is storedat the AP, and/or whether a frame including the CSI would be too longfor transmission, for example as described above.

Moving to step 2206, a communication comprising an indicator isgenerated. A length of the communication is based on the determinationin step 2204. For example, a CSI feedback field may be omitted to makethe communication a certain length. Further, a value of the indicator isbased on a condition that caused the channel state information not to betransmitted. The indicator may comprise a difference CSI field, a useprevious SF field, and/or a portion of a CSI null and difference field,for example. The indicator may further comprise a bit, field, or othersignifier indicative of whether a transmission limitation would beexceeded by transmitting the channel state information The generation,and/or a determination of the length or value of the indicator may bedetermined by the CSI feedback module 1704, for example. Thecommunication may comprise CSI feedback, for example the CSI feedback408, or another communication indicating that CSI will not betransmitted. The indicator may be included in a control field of the CSIfeedback.

At step 2208, the communication is transmitted. The communication may betransmitted using the transmitting module 1708, for example.

FIG. 23 illustrates an aspect 2300 of a method for communication. Themethod may be implemented by the AP 1200, for example, to determine thatchannel state information will not be received, and to determine why thechannel state information is not being transmitted from an STA. Althoughthe method below will be described with respect to elements of the AP1200, those of skill in the art will appreciate that other componentsmay be used to implement one or more of the steps described herein.

At step 2302, a request for channel state information is transmitted,for example by the transmitting module 1306. Thereafter, at step 2304, acommunication is received. The communication may comprise a first fieldfor indicating if a first segment of channel state information is beingreceived in the communication, and a second field for indicating anumber of segments of the channel state information remaining to bereceived. The first and second field may be portions of a reservedfield, such as a first segment field and a remaining segments field. Thecommunication may be received using the receiving module 1304, forexample.

After reception of the communication, it is determined whether thecommunication includes channel state information based on the firstfield and the second field at step 2306. For example, it may bedetermined that no channel state information is included in thecommunication if the first field indicates that a first segment ofchannel state information is not included in the communication and avalue of the second field is at least as great as a maximum number ofremaining segments.

Further, at step 2308, a condition that caused the channel stateinformation not to be received is determined if the first field and thesecond field indicate that the communication does not include channelstate information. The condition may be determined based at least inpart on two or more bits adjacent to the first field or the secondfield. For example, bits that may be used for a different purpose maybecome reserved when the first field and second field indicate that thecommunication does not include the channel state information, asdescribed above with respect to FIG. 12. The determining at step the2306 and/or at the step 2308 may be performed by the CSI processingmodule 1314, for example.

FIG. 24 illustrates an aspect 2400 of a method for communication. Themethod may be implemented by the STA 1700, for example, to determinewhether to transmit CSI, and to indicate to an AP a reason why CSI isn'tbeing transmitted. Although the method below will be described withrespect to elements of the STA 1700, those of skill in the art willappreciate that other components may be used to implement one or more ofthe steps described herein.

At step 2402, a message indicating that channel state information isrequested is received, for example using the receiving module 1702. Insome aspects, the message comprises an NDPA frame or a polling message.The message may indicate whether previously transmitted SF is stored atan AP.

Thereafter, at step 2404 a communication is generated. The communicationmay comprise a first field for indicating if a first segment of channelstate information is being transmitted and a second field for indicatinga number of segments of the channel state information remaining to betransmitted. The first and second field may be portions of a reservedfield, such as a first segment field and a remaining segments field Thegeneration may be performed by the CSI feedback module 1704, forexample. The CSI feedback module 1704 may evaluate whether a channelcondition has changed, whether CSI is stored at the AP, and/or whether aframe including the CSI would be too long for transmission, for exampleas described above. The communication may comprise CSI feedback, forexample the CSI feedback 408.

Moving to step 2406, a plurality of bits in the communication is set ifto signify a condition that caused the channel state information not tobe included if the first field and the second field indicate that thecommunication does not include channel state information. The pluralityof bits may signify that a previous request for channel stateinformation was not received, that current channel state information issubstantially similar to previously transmitted channel stateinformation, or that a transmission limitation would be exceeded bytransmitting the channel state information, for example. The setting ofthe plurality of bits may be performed by the CSI feedback module 1704,for example. The plurality of bits may be included in a control field ofthe CSI feedback.

At step 2408, the communication is transmitted. The communication may betransmitted using the transmitting module 1708, for example.

Those of skill in the art will appreciate that a simple and clean frameformat for CSI feedback communications has been described herein. Insome aspects, STA AIDs may be indicated in the NDPA. There may be noindication about a number of STAs in the NDPA in some aspects, althoughthis information may be inferred from the length of NDPA. In someaspects, information regarding whether SF has been received or stored atan AP may be included in the NDPA. In some aspects, informationregarding whether an STA is transmitting CSI is included in CSI feedbacktransmitted to the AP. In some aspects, a wrapper is used to indicateparameters for an STA to use when transmitting SF.

In some aspects, no field is specified for a “first responder” STA. Thefirst listed STA-AID may implicitly represent the first responder in oneaspect. NDPA and CSI Poll may carry a matching sequence number to enableSTAs to match a CSI Poll to a corresponding NDPA. Similarly, thesequence number may be copied into a control field transmitted by theSTA.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrate circuit (ASIC), or processor. Generally,where there are operations, module, or steps illustrated in Figures,those operations may have corresponding counterpart means-plus-functioncomponents. For example, a user terminal may comprise means fordetermining a modulation coding scheme (MCS) or a rate for receivingchannel state information and means for transmitting a wrapper framecomprising a control field indicating the determined MCS and at leastone field indicating that at least a portion of channel stateinformation is requested.

FIG. 25 illustrates a block diagram of an example user terminal 2500 inaccordance with certain aspects of the present disclosure. User terminal2500 comprises a determining module 2510 which may be configured toperform the functions of the means for determining discussed above. Insome aspects, the determining module may correspond to the controller280 of FIG. 2. User terminal 2500 further comprises a transmittingmodule 2515 which may be configured to perform the functions of themeans for transmitting discussed above. In some aspects, thetransmitting module may correspond to one or more of the transmitters254 of FIG. 2.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An apparatus for wireless communication,comprising: a processing system configured to determine a rate forreceiving channel state information; and a transmitter configured totransmit a frame comprising a control field indicating the determinedrate and at least one field indicating that at least a portion ofchannel state information is requested, wherein at least a first segmentof the channel state information was received in a previous frame andwherein the at least one field comprises at least a first fieldindicating a number of segments of the channel state informationremaining to be received in one or more subsequent frames.
 2. Theapparatus of claim 1, wherein the processing system is configured todetermine the rate for receiving the channel state information based ona change of a state of a communication channel for which the at least aportion of channel state information is requested.
 3. The apparatus ofclaim 1, wherein the rate comprises a physical layer (PHY) rate.
 4. Theapparatus of claim 1, wherein the at least one field comprises one ormore fields of a null data packet announcement.
 5. The apparatus ofclaim 1, wherein the at least one field comprises one or more fields ofa polling message.
 6. The apparatus of claim 1, wherein the framefurther comprises at least one of a frame control field that isdifferent than the control field, a duration field, a destinationaddress field, a carried frame control, a source address field, or acyclic redundancy check field.
 7. The apparatus of claim 1, wherein theframe further comprises a first field comprising at least one of a firstsubfield representing an association identifier for another apparatusfrom which the channel state information is requested, a second subfieldrepresenting a number of spatial streams of the channel stateinformation that is requested, a third subfield representing a groupingof tones for which the channel state information is requested, a fourthsubfield representing a coefficient size corresponding to a quantizationused for entries in a matrix representative of the channel stateinformation, a fifth subfield representing a quantization for angles tobe used for the channel state information, or a sixth subfield includingbits that are reserved.
 8. The apparatus of claim 1, wherein the framefurther comprises a basic service set identifier field.
 9. A method ofwireless communication, comprising: determining a rate for receivingchannel state information; and transmitting a frame comprising a controlfield indicating the determined rate and at least one field indicatingthat at least a portion of channel state information is requested,wherein at least a first segment of the channel state information wasreceived in a previous frame and wherein the at least one fieldcomprises at least a first field indicating a number of segments of thechannel state information remaining to be received in one or moresubsequent frames.
 10. The method of claim 9, further comprisingdetermining the rate for receiving the channel state information basedon a change of a state of a communication channel for which the at leasta portion of channel state information is requested.
 11. The method ofclaim 9, wherein the rate comprises a physical layer (PHY) rate.
 12. Themethod of claim 9, wherein the at least one field comprises one or morefields of a null data packet announcement.
 13. The method of claim 9,wherein the at least one field comprises one or more fields of a pollingmessage.
 14. The method of claim 9, wherein the frame further comprisesat least one of a frame control field that is different than the controlfield, a duration field, a destination address field, a carried framecontrol, a source address field, or a cyclic redundancy check field. 15.The method of claim 9, wherein the frame further comprises a first fieldcomprising at least one of a first subfield representing an associationidentifier for an apparatus from which the channel state information isrequested, a second subfield representing a number of spatial streams ofthe channel state information that is requested, a third subfieldrepresenting a grouping of tones for which the channel state informationis requested, a fourth subfield representing a coefficient sizecorresponding to a quantization used for entries in a matrixrepresentative of the channel state information, a fifth subfieldrepresenting a quantization for angles to be used for the channel stateinformation, or a sixth subfield including bits that are reserved. 16.The method of claim 9, wherein the frame further comprises a basicservice set identifier field.
 17. An apparatus for wirelesscommunication, comprising: means for determining a rate for receivingchannel state information; and means for transmitting a frame comprisinga control field indicating the determined rate and at least one fieldindicating that at least a portion of channel state information isrequested, wherein at least a first segment of the channel stateinformation was received in a previous frame and wherein the at leastone field comprises at least a first field indicating a number ofsegments of the channel state information remaining to be received inone or more subsequent frames.
 18. The apparatus of claim 17, furthercomprising means for determining the rate for receiving the channelstate information based on a change of a state of a communicationchannel for which the at least a portion of channel state information isrequested.
 19. The apparatus of claim 17, wherein the rate comprises aphysical layer (PHY) rate.
 20. The apparatus of claim 17, wherein the atleast one field comprises one or more fields of a null data packetannouncement.
 21. The apparatus of claim 17, wherein the at least onefield comprises one or more fields of a polling message.
 22. Theapparatus of claim 17, wherein the frame further comprises at least oneof a frame control field that is different than the control field, aduration field, a destination address field, a carried frame control, asource address field, or a cyclic redundancy check field.
 23. Theapparatus of claim 17, wherein the frame further comprises a first fieldcomprising at least one of a first subfield representing an associationidentifier for an apparatus from which the channel state information isrequested, a second subfield representing a number of spatial streams ofthe channel state information that is requested, a third subfieldrepresenting a grouping of tones for which the channel state informationis requested, a fourth subfield representing a coefficient sizecorresponding to a quantization used for entries in a matrixrepresentative of the channel state information, a fifth subfieldrepresenting a quantization for angles to be used for the channel stateinformation, or a sixth subfield including bits that are reserved. 24.The apparatus of claim 17, wherein the frame further comprises a basicservice set identifier field.
 25. A non-transitory computer readablemedium comprising instructions that when executed cause an apparatus to:determine a rate for receiving channel state information; and transmit aframe comprising a control field indicating the determined rate and atleast one field indicating that at least a portion of channel stateinformation is requested, wherein at least a first segment of thechannel state information was received in a previous frame and whereinthe at least one field comprises at least a first field indicating anumber of segments of the channel state information remaining to bereceived in one or more subsequent frames.
 26. An access point forwireless communication, comprising: an antenna; a processing systemconfigured to determine a rate for receiving channel state information;and a transmitter configured to transmit, via the antenna, a framecomprising a control field indicating the determined rate and at leastone field indicating that at least a portion of channel stateinformation is requested, wherein at least a first segment of thechannel state information was received in a previous frame and whereinthe at least one field comprises at least a first field indicating anumber of segments of the channel state information remaining to bereceived in one or more subsequent frames.